This doesn’t look like an Ubuntu bug to me. It looks like the classic dual-boot RTC issue where Linux and Windows disagree on how the hardware clock should be interpreted.
Linux normally stores the RTC in UTC, while Windows assumes the RTC contains local time. As a result, Ubuntu shows the correct time, but Windows can end up several hours off until it performs a manual synchronization. The fact that Ubuntu is consistently correct and Windows immediately fixes itself after a sync is a strong indicator that this is what you’re running into.
I would leave the BIOS clock set to UTC and configure Windows to treat the hardware clock as UTC as well. On Windows, open an elevated Command Prompt and run:
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation" /v RealTimeIsUniversal /t REG_DWORD /d 1 /f
Then reboot Windows. This is a well-known fix for dual-boot systems and avoids the drawbacks of forcing Linux to use local time, especially when daylight saving time changes are involved.
After rebooting, verify that Windows is still set to the correct time zone and that automatic time synchronization remains enabled. If everything is configured correctly, both operating systems should continue showing the correct time without requiring manual resynchronization after switching between Ubuntu and Windows.