Facing this exact issue on two (non-preview now) system at home, one was cloned from the SSD of the other and I just changed the name and Windows license etc and has been working fine for years until now...all file/printer sharing and RDP is dead, just keeps saying incorrect user/pass. All the normal stuff is verified, private network, sharing on, etc etc and certain it is due to the update plus same SID as follows:
I verified both machines do have the same SID.
I tried uninstalling KB5065426 from both systems but that did not resolve.
Next I removed KB5064081 from both systems and reboot and now SMB/RDP is working normally again.
In my process of troubleshooting I found that the Remote Desktop Classic Windows app actually still worked also but, the regular RDP would not, so the RDP Classic app must authenticate differently? I'm not sure if you can even get or install this still since the newer "Remote Desktop" app is depreciated and maybe not working at all.
I am considering trying SIDCHG on one of them as a long term solution since I assume Microsoft will not make any attempt to revert this dispite what will likely be millions of impacted systems. Please us know if you tries SIDCHG and any problems or side effects or other issues are encountered.