Try to configure your project in PhpStorm

1. Open Settings->Languages & Frameworks->PHP->Debug
2. Uncheck the "Ignore external connections through unregistered server configurations" option
3. OK

I cannot stress enough the importance of one of the remarks - "Don't forget to set the cookie for xdebug". I had everything right and my debugger still wouldn't attach due to this. One recommendation I can make is to install xdebug helper chrome extension. Once you have it, start the debug from PhpStorm, navigate to the page you want to debug and turn on the debug setting in the extension by clicking the "bug" icon within address bar.

The problem was fixed by adding the break points to other parts of the code as it was not working when attached to the try clause. Additionally, here are some other tips that might be useful:

1. Try using a programmatic breakpoint: xdebug_break();
2. Check that if your php is 32bit then so is the version of Xdebug (or that they are both 64 bit).
3. The xdebug remote host setting relates to the server IP address (so 127.0.0.1 for local).

Xdebug 3 will be fully supported in PhpStorm 2020.3 version only, which is currently in EAP stage (Early Access Program) and will be released in about 1 month time.

It is already supported in the most recent EAP #6 build: check this blog post for more info: https://blog.jetbrains.com/phpstorm/2020/11/phpstorm-2020-3-eap-6/

I have downloaded Xdebug 3.0.0beta1 for my PHP 7.4 on Windows 10, configured it from scratch (using correct Xdebug 3 config values: https://3.xdebug.org/docs/upgrade_guide and https://3.xdebug.org/docs/all_settings) ... and it still works fine in PhpStorm 2020.2.3.

Yes, IDE sends old-style parameters when initiating debugging for a CLI script (like xdebug.remote_{host, port} etc) but the debug still works just fine.

This is my php.ini content for Xdebug 3 settings (as simple as this):

[xdebug]
xdebug.client_host = 127.0.0.1
xdebug.client_port = 9001
xdebug.mode = debug

(I have a bit mores settings, but those are customisation for output file names, log locations, extra stuff for quickly turn on some options in some scenarios/when needed etc -- these are not needed here and it works fine without them)

CLI debug initiated from IDE ("PHP Script" type of configuration):

That's what IDE is executing: E:\Projects\php\php74\php.exe -dxdebug.remote_enable=1 -dxdebug.remote_mode=req -dxdebug.remote_port=9001 -dxdebug.remote_host=127.0.0.1 E:\Projects\web\_idetest\test.php. As you may see these old style parameters do not affect Xdebug 3 at all.

P.S. If I set xdebug.start_with_request = yes in php.ini then debug will work even for Run (or when executing that PHP script outside of IDE) -- as long as "phone handle" icon is green (IDE listens for incoming debug requests).