You need to set up your global core.excludesfile configuration file to point to this global ignore file e.g:
*nix or Windows git bash:
git config --global core.excludesFile '~/.gitignore'
Windows cmd:
git config --global core.excludesFile "%USERPROFILE%\.gitignore"
Windows PowerShell:
git config --global core.excludesFile "$Env:USERPROFILE\.gitignore"
For Windows it is set to the location C:\Users\%username%\.gitignore. You can verify that the config value is correct by doing:
git config --global core.excludesFile
The result should be the expanded path to your user profile’s .gitignore. Ensure that the value does not contain the unexpanded %USERPROFILE% string.
Important: The above commands will only set the location of the ignore file that git will use. The file has to still be manually created in that location and populated with the ignore list. (from muruge’s comment)
You can read about the command at https://docs.github.com/en/get-started/getting-started-with-git/ignoring-files#configuring-ignored-files-for-all-repositories-on-your-computer