Find which .net versions you have

On Windows 10 or 11

reg query "HKLM\SOFTWARE\Microsoft\Net Framework Setup\NDP" /s | 
	? { $_ -like "*version*" } | 
	% { ($_ -split " ") | 
	? { $_ -match "[0-9.]+" } | 
			% { $_ } 
		} |
	sort -desc |
	unique

Gives output such as --

4.8.09032
4.0.0.0
4.0.0
3.5.30729.4926
3.0.6920.4902
3.0.4506.4926
3.0.4203.4926
3.0.30729.4926
3.0.0.0
2.0.50727.4927

Windows - looking for .net version post "framework"

dotnet --list-runtimes

On ubuntu linux

dpkg --get-selections | grep -v deinstall | grep dot