Bazzite has a command, `ujust setup-boot-windows-steam`, which when run adds an entry to Steam-in-Bazzite that causes a Windows boot.

It also has a command `ujust regenerate-grub` which adds a Windows entry to the bootloader.

Each of these is a single command which only must be run one time after install. I suppose it could take a few hours to either do it by hand, or to discover one of these options, but they are both documented and in particular the guide at https://docs.bazzite.gg/General/Installation_Guide/dual_boot... (which you implied you followed) mentions the latter command.

It works on each of my Bazzite machines without any manual tinkering/intervention. Not sure why it would not Work On Your Machine (TM).