If you are looking for standard "one-tap" functionality already built into GMod, you can use:
: Accessible via the "Workshop" button in the Steam overlay (Shift+Tab) to find and download addons instantly. Onetap Gmod Download
The most prominent feature associated with Onetap tools for GMod is the ability to without needing a Steam account or client. Key Useful Features If you are looking for standard "one-tap" functionality
These tutorials demonstrate the standard one-click methods for downloading and installing GMod addons: How To Get Mods In Garry's Mod (Gmod) - Step By Step YouTube · GuideRealm Onetap Gmod Download