I downgraded to 2021.09.1 build 372
Sessioninfo still reports codepage 65001 and Unicode issue is also affecting previous version (build 372) in similar way
It seams codepage 65001 is the problem. My guess is this has changed with a recent windows update - to something Rstudio doesn’t like
Updated
I found a solution that at least on my PC works 
In windows controlpanel change region settings current system locale to "Latin (World)" and make sure "Beta: Use Unicode UTF-8...." in not checked.
I had to restart PC and login with adm. rights to make the change
After this Rstudio works as before. And sessionInfo() don't report codepage 65001 anymore
Brgds. Henrik