I feel foolish because I figured it out right after posting, but I figured I'd share because it isn't intuitive and hopefully this will save someone some time.

The package you want to install is not gcc. You want to install gcc-toolset-9. You will notice after installation that you will still get 8.x if you do a gcc --version. gcc-toolset-9 installs to /opt. The idea is to give you a separate development environment. See this documentation. After installation you can run the updated gcc with /opt/rh/gcc-toolset-9/<username>/bin/gcc.

As @Stephen Kitt pointed out, you can actually get a shell with the updated toolset by running scl enable gcc-toolset-9 bash. Running this command will open a new bash session with the environment variables appropriately updated.

You can also run gcc v.9 directly with scl enable gcc-toolset-9 gcc <your_gcc_args>. See this documentation for details.

To install newer versions of GCC on RHEL, you should install the relevant GCC toolset. Toolsets are available for each major GCC release stream; they are all co-installable and don’t replace the system GCC.

Currently the best option is GCC toolset 15 which is supported until November 2029.

On a system with access to RHEL repositories (online or through Satellite for example), install the toolset with

sudo yum install gcc-toolset-15

or

sudo dnf install gcc-toolset-15

To compile C++17 code, you’d use

scl enable gcc-toolset-15 g++ …

(GCC 15 defaults to C++17 with GNU extensions).

For offline installation see How to use yum to get all RPMs required, for offline use?

in a nutshell, here are some examples for how to install and configure

• for python3 to get python3.9: dnf install -y python39 && alternatives --set python3 $(command -v python3.9)
• for gcc to get gcc-12: dnf install gcc-toolset-12 && source scl_source enable gcc-toolset-12
• for java to get java-17: dnf install java-17 && bin_java_filename=$(rpm -qa|grep java-17|xargs rpm -ql|grep "bin\/java$"|head -1) && alternatives --set java ${bin_java_filename}
• tested on rocky8, rocky9

which repo has the newer software versions?

• the old method using "SCL" was deprecated
• the new method is to use a repo called "appstream"
• here is a post written by the distro maintainers explaining the change https://developers.redhat.com/blog/2018/11/15/rhel8-introducing-appstreams
• the repo is enabled by default

how to: install newer software versions?

• for python3: dnf install python39
• for gcc: dnf install gcc-toolset-12

how to: change the system default?

• for python3: alternatives --set python3 $(command -v python3.9)
• for gcc:
  • edit your user .bashrc or .bash_profile or create a new file under /etc/profile.d/ with the following: source scl_source enable gcc-toolset-12
  • i thought scl_source would go away in el8, el9 but apparently not
  • for more info on scl_source go to this link https://unix.stackexchange.com/a/195219/5510 or Permanently enable RHEL scl

p.s. what is the difference between alternatives and update-alternatives?

• the original tool is called update-alternatives and is from Debian linux distro
• in EnterpriseLinux, Redhat rewrote the tool and called it alternatives and when you install alternatives the package also installs a symlink with name update-alternatives on your env var PATH to help you find the tool
• the two are similar but not the same because their source code is different

This is not recommended but you can install version 11.3 by downloading gcc-11 (version 11.3) from here. And downloading the dependencies gcc-11-base and libgcc-11-dev.

Then, run sudo apt install /path/to/file where /path/to/file is the path to the actual downloaded file. If it can't find the file, you may need to put it in double quotes like "/path/to/file".

You will need to install the gcc-11-base package first, then libgcc-11-dev and finally, gcc-11.

For example, if it's downloaded to your Downloads directory:

sudo apt install $HOME/Downloads/gcc-11-base_11.3.0-6ubuntu1_amd64.deb

and

sudo apt install $HOME/Downloads/libgcc-11-dev_11.3.0-6ubuntu1_amd64.deb

and

sudo apt install $HOME/Downloads/gcc-11_11.3.0-6ubuntu1_amd64.deb

I'm pretty sure gcc only requires gcc-11 >11.2 so this should downgrade your version of gcc and when you're done compiling or whatever you need it for, simply run:

sudo apt update
sudo apt install --reinstall gcc-11 gcc-11-base libgcc-11-dev

to upgrade back to the current version of gcc-11 (11.4).

Granted, the installation isn't guaranteed to work, could be insecure or lacking security updates. Also, you may run into dependency issues. If that's the case, you'd have to tread carefully or install each dependency one by one but always pay attention to what, if any, packages would need to uninstall when installing weird versions because you don't want to inadvertently uninstall a bunch of stuff you want or need.

EDIT: you will need to install dependencies (included above) but you can run the following commands to do it more quickly.

Run the following commands to create a working directory and download the packages:

cd
mkdir GCC11.3
cd GCC11.3
wget 'http://mirrors.kernel.org/ubuntu/pool/main/g/gcc-11/gcc-11-base_11.3.0-6ubuntu1_amd64.deb'
wget 'http://mirrors.kernel.org/ubuntu/pool/main/g/gcc-11/libgcc-11-dev_11.3.0-6ubuntu1_amd64.deb'
wget 'http://mirrors.kernel.org/ubuntu/pool/universe/g/gcc-11/gcc-11_11.3.0-6ubuntu1_amd64.deb'

Now, install the packages. Again, however, remember to pay attention to what, if any packages will be uninstalled when you install these weird versions. Review the list before you select Y to accept the changes!:

sudo apt install ./gcc*.deb

And again, when you're done compiling or whatever you need gcc 11.3 for, simply run:

sudo apt install --reinstall gcc-11 gcc-11-base libgcc-dev

to upgrade back to gcc 11.4.

According to the man page for gcc-toolset-11, it only supports the enable command. It also states that you can run scl gcc-toolset-11 enable bash to execute the bash command with the gcc-toolset-11 environment, which should be equivalent to what the load command would do.

Example:

[root@localhost ~]# scl enable gcc-toolset-11 bash
[root@localhost ~]# gcc --version
gcc (GCC) 11.2.1 20220127 (Red Hat 11.2.1-9.1.0.3)
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[root@localhost ~]# exit
exit
[root@localhost ~]# gcc --version
gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-18.0.2)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

[root@localhost ~]#