My Garmin watch is connected to the connect app, but not to the connect website. How do I connect it to the website?
In that case, I'd make sure you're logged in using the same Garmin credentials used to login to the app.
On Gamin Connect Web go to Account Information - https://connect.garmin.com/modern/settings/accountInformation
Take note of the email address being used.

Go to the app, Settings, Device Sync Audit. Make sure it matches.
If still issues, contact Garmin Product Support directly.