EDIT: Based on comments in Password Autofill extensions in Big Sur?, it sounds like this may be used for auto-type implementation (feature 158).
Sadly, I have a feeling that the size of Bitwarden’s customer base that are specifically “macOS + Big Sur + Safari” users isn’t big enough to prioritize this feature over other cross-platform feature requests like Overlay popup interface and Auto-type/Autofill for logging into other desktop apps.
Probably need to hope that an external contributor would be interested enough to work on this and open a PR.
Competitors that support this appear to be Apple-first like:
Strongbox - only Apple devices (iOS + macOS)
- 1Password (? EDIT: not too sure of status based on blog post) - originally only for Apple users before becoming cross-platform