(1) OK, that's right, you have to boot to Windows in order to do an upgrade/repair-install. And it can't even be Safe Mode. So you definitely need that password, unless that trick you found will work. I've read they don't work anymore, not since the early days of Win 10. But I am too honest & straight-laced to ever know for sure.
(2) "But, now I even more want to know how to boot to Advanced Recovery on my Gateway, I would be able to boot to DVD or USB without having to deal with bios switching from UEFI to Legacy."
I clearly recall I had a problem booting DVD on this Dell Inspiron 3542 early on. There was a boot item for it that showed up whenever I went to the BIOS Boot Option menu (F12) whether I had a DVD inserted or not. That worked for my DiscWizard Bootable Media, but not for a Windows Installation DVD.
So I constructed a boot item for the Installation DVD in BIOS Setup at the Boot screen by clicking "File Browser Add Boot Item". I can't quite recall the choices there, but I guess I went for Setup.exe. It worked to boot my Installation DVD, but I never knew whether that constituted an actual UEFI boot.
Then, using "File Browser Del Boot Item", I deleted that one & also deleted the original one. After that, nothing showed up when I did F12 -- unless I had a DVD inserted into the drive. But the one that shows up then boots both the DiscWizard CD & a Windows Installation DVD.
But I know nothing of Gateway.