Fn+F does the job! It will maximize and minimize to a full-screen application.
Answer from Rob Kley on Stack ExchangeRestore a minimized window from Dock - how to - MPU Talk
macos - Maximize window shortcut - Ask Different
How to "maximze" window size but still within dock and menu bar? - Ask Different
is there a shortcut to maximize a window? | MacRumors Forums
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One thing that always bothered me about MacOS was that I had to click the dock icon to restore a minimized window. It wasn't until today that I learned the keyboard shortcut. Apologies for those that already knew but maybe this helps someone from this minor annoying inconvenience.
To re-open the minimized window, go to the window that you want to "maximize" by windows navigation keyboard shortcut command + tab. Release only tab button.
Keep pressing command button and press option button. Now pressing option button release command button, the window will be maximized*.
EDIT: I learned that it's quicker that after releasing the Tab button, I SLIDE my thumb from the Command button to the Option button
*Maximize in the Windows-sense...not the "fill your screen" sense
Fn+F does the job! It will maximize and minimize to a full-screen application.
Using macOS 15.2 Sequoia here.
The menu item window->fill, defaults to ⌃F (Ctrl+Fn+f), should do what you want.
The item window->center ⌃C (Ctrl+Fn+c) restores the original size and centers the window.
Menu item window->minimize ⌘M (Cmd+m) minimizes the window.
To remove the spacing around the "filled" window, you have to go to System Settings -> "Desktop & Dock" -> disable the option "Tiled windows have margins"
Assign a shortcut for the Zoom menu item (or whatever it's called in your locale) from System Preferences:

If you want the shortcut to always maximize a window to fill a screen, you can use for example Spectacle:

Or add a line like this to ~/.slate with Slate:
bind m:cmd;shift move screenOriginX;screenOriginY screenSizeX;screenSizeY
I have used FastScripts to assign a shortcut to this script:
try
tell application "Finder" to set b to bounds of window of desktop
try
tell application (path to frontmost application as text)
set bounds of window 1 to {item 1 of b, 22, item 3 of b, item 4 of b}
end tell
on error
tell application "System Events" to tell window 1 of (process 1 where it is frontmost)
try
set position to {0, 22}
set size to {item 3 of b, (item 4 of b) - 22}
on error
click (button 1 of window 1 where subrole is "AXZoomButton")
end try
end tell
end try
end try
When you tell System Events to change the position and size through the accessibility API, there is a noticeable delay between when the position and the size are changed. Telling the application to change the bounds of a window is faster but it doesn't work with all applications. Other applications like Slate and Moom always use the accessiblity API.
Sorry I made a mistake about minimizing window. It's ready from Apple. So, I amended.
Answer:
- Command-M :Minimize the active window to the Dock
- Command-Option-M :Minimize all windows of the active application to the Dock
- (Setup is required) :Maximize the active window
To maximize the active window(application), you must assign the operation to shortcut key as follows;
- Go to System Preferences>Keyboard>Shortcuts>App Shortcut, then click "+" to add shortcut key.
- Choose "All Application" which means this change will affect all application, put the text "Maximize" in "Menu Title" textbox and press "Command+Shift+M" in "Shortcut Key" textbox.
- Restart Window(Application) which you would like to affect by the shortcut key.(No reboot requred)
- You will find new menu item in the menu bar also.
Recommendation basis:
I recommend you to use below shortcut key instead of using default minimizing shortcut key.
To Minimize the active window(application):
Command+H :Hide active window(application)
It's possible to minimize the active window in above shortcut key but actually it's hidden the active window(application). And, if you use this shortcut key, you can switch hidden window by shortcut key which is "Command + Tab" quickly. If you minimize the active window by Command+M, you can not switch application by command + Tab quickly and you have to click the application from Dock.)
You can refer related information in below.
http://support.apple.com/kb/HT1343, http://support.apple.com/kb/PH13911
One of the default settings in System Preferences > Dock is [√] Double-click a window's title bar to zoom; however by default, e.g., Finder does not have a keyboard shortcut to zoom a window.
One may add a keyboard shortcut for the Finder > Window > Zoom command in System Preferences > Keyboard > Shortcuts > App Shortcuts, as shown in the image below.
Note that one can also choose All Application and use the following as the menu title,
e.g. Window->Zoom so as not to confuse it with another Zoom command elsewhere in its menu system if applicable.
Have a look at: Create keyboard shortcuts for apps on Mac
Click the [+] and fill in the sheet, then click the Add button:

The previous answers do work, of course. The problem is that sometimes maximizing the window isn't the same as having the window full-sized on your desktop.
There is an app on the Mac App Store called "Magnet" (https://apps.apple.com/at/app/magnet/id441258766?mt=12) which does this job perfectly and you can even customize the shortcuts.
Opt ⌥ green dot & also the double-click title bar both kind of maximise, but it won't always fill the entire screen. Depending on the document type, it may just fill top to bottom, but not full width.
To make it fill the entire screen, Opt ⌥ double click any window corner, once the cursor turns into a double arrow. This will stop short of the Dock, if you have it always visible, otherwise fill the whole screen.

Opt ⌥ double-click is actually quite flexible. If you use it on one edge of a window it will expand to fit, but just in that direction, horizontal or vertical.
If you Opt ⌥ drag by either an edge or a corner, opposite sides or the entire window will resize equally.
Actually probably the easiest thing to do would be to double-click a window's title bar to maximize the window. You can set this in your System Preferences.

Command + Tab until you get the app's icon.
Before releasing the Command key, press and hold the Option key.
You must switch to another app and let it take focus first. In other words, you can't just Command + Tab to another app and before actually selecting that app (by releasing the Command and Tab keys), switch right back to your minimized app, which you might attempt to do if you minimized it by accident or just simply changed your mind shortly after minimizing.
Both the Command and left Option keys must be pressed on the same side (left or right) of the keyboard.
To restore one of many minimized windows using only the keyboard, you have two choices:
While using Cmd + tab (eg. changing applications):
- Start with a minimized window
- Cmd + tab to the application icon (Continue to hold Cmd)
- While holding Cmd, push the ↑ (or ↓) arrow key on the keyboard. This will bring up a list of all the application's windows (You can release key command key once the window list view comes up if you like)
- Push the down arrow key (↓) to select the minimized windows.
- Use the left and right arrow keys (← or →) to select the minimized window you want
- Push Return or Enter to restore the window and bring it into focus (make it the selected window)
(Tested on OS X Mountain Lion)
Or,
Directly when the application is already the current application:
Steps as above, but instead of steps 2 and 3 (Cmd + tab and arrow keys):
- Start with a minimized window
- Control + ↓. If App Exposé is selected in Trackpad preferences, you can also swipe down with three fingers.
OS X Mountain Lion "Keyboard" preferences have a "Mission Control" keyboard shortcut for this:

Hold down alt/option and double click in the corner (where you would drag to resize).
Is this something everybody but me knew all along?