The question description is self-explanatory, I guess it's a bug, and the 1password team should take a look at it.
I use the latest Chrome version (Version 91.0.4472.164 (Official Build) (x86_64)) on macOS Big Sur.
Here's the video of the extension misbehaving.
1Password Version: 1Password 7 Version 7.8.6 (70806001) 1Password Sto
Extension Version: 18.104.22.168
OS Version: macOS Big Sur (11.4 (20F71))
Sync Type: No idea
Referrer: forum-search:Mac 1password opens the website URL instead of autofilling the login details.