Sometimes the link between Chrome and your torrent client gets "stuck" in the Windows Registry. You can manually reset this to force Chrome to recognize magnet links again. Press Windows Key + R, type regedit, and hit Enter.
Which are you on (Windows 11, macOS, etc.)? Can't open magnet URL with Google Chrome anymore
Select Cookies and other site data and Cached images and files. Click Clear data. Restart Chrome and try the link again. Check for Conflicting Extensions