It's a pain, I know. In case anybody is interested: Solving the Ubuntu-Windows Dual Boot Time Discrepancy | by Lakpahana AGS | Medium.
I've just applied the Linux command and tested it. The Windows time now stays the same when switching back and forth between Linux and Windows. One day I will try to understand the exact why.
OS is the latest Ubuntu (24.04 I think) installed on an external harddisk.