The absolute bane of my existence, I had a time a week ago repairing my bootloader after I (stupidly) did 3 months of windows updates after running a bunch of disk repairs and other recovery based things after I (again, stupidly) fell for a fake repo for deepseek tui and infected myself
For Windows CMD+R menu, run it by pressing CTRL+SHIFT+Enter (elevates to admin). You may have to do it twice for some unknown reasons after reinstalling the OS.
Had to learn this recently when my wife’s computer refused to register requests to boot into bios despite spamming F12 / Del many different times across many different USB ports. Such a pain in the ass.