Agreed. Windows updates will very likely break your single-drive dual-boot at some point. So, use two different drives and use your bios/efi to choose which one to boot.
Edit: check out https://hackaday.com/2021/11/30/linux-fu-the-ultimate-dual-boot-laptop/
Edit 2: Framework 16 looks like it would meet your needs. It has two M.2 sockets for drives. https://frame.work/products/laptop16-diy-amd-7040
How much money did you spend, and how much time overall? Would you do it again?