I’m committed right now to a Win 10 AME and EndeavourOS Dual Boot, and back when I first started running such a setup, Windows (8, 8.1, 10) would always overwrite the boot sector with it’s own loader when installed. You can get a dual boot from grub working by deliberately partitioning before installing Windows, then whichever Linux, making sure to install grub during. I gave up on that hassle after one round and now I just use separate drives for each OS.