Still showing as 10.15.

[wellander1]

In Monterey beta 1 the User agent string in in Safari on my M1 Mac shows this Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.0 Safari/605.1.15
Will this ever be fixed?

 

[Ritsuka]

No, that's an intentional decision, it's not a bug.

 

[DeltaMac]

This has been ongoing since Big Sur betas.
I don't claim to understand the technical details - but it appears to be a problem with the internet, and how it does not seem to know how to respond properly to a user agent system version 11 (and later)
So, apparently macOS simply continues to use a string with the latest macOS version that makes it all function properly.
Presently, that would be what you see: 10_15_7

216593 – [macOS] Limit reported macOS release to 10.15 series

bugs.webkit.org

Next step should have been 10_16_0 , but that's not really correct, either. So, now (someone who takes care of that stuff for the whole internet) is probably working out a solution that reliably works for everyone, in all (or most) situations.
And, the fix is likely way beyond Apple's paygrade.