I was in your same condition. As this site has more results than official Acer forums I just add the missing bit here.
some new models have the AHCI/RST option hidden in bios.
by pressing Ctrl+S in the relevant BIOS page the option appears.
Now: which is the relevant page? it depends on your model, in my case it was the second page, where, among other things there was a set of other options for boot.
Also I want to point out that the proposed method to reset the boot loader of windows failed miserably: I've completed all the steps from within windows (edit the registry),
but bcdedit failed all the described tentatives and windows was stucking without a proper boot.
Still, after installing ubuntu 20.04.1 (mate edition) and GRUB, I was able to use grub to boot windows properly!!!
Note: I've shrunk the windows main partition (labeled C:) from within Windows itself to make room to ubuntu and keep all other geometries untouched (even if I do not know how to use the repair partition now :/)