Sorry to confuse. You figured it out right. "Advanced Startup" is the recovery environment where the first screen is "Choose an Option". So, I often say "recovery environment (Choose an Option)" for that. I also say "Shift+Restart (or whatever)". The "whatever" refers to the long way you must do it: "START, Settings, Update & Security, Recovery, Restart now (under Advanced startup)". From now on I'll call it "Advanced startup", if I can remember. But those are all the same. (And did you try the other Shift key?)
But you see the letters can be different there. (The worst is when C: is different. Was it?) That's why I added the "damn" part. I left the earlier stuff in because it might have still been R. But you figured it right. Too bad the situation hasn't improved.
I'm not sure what fixed it for me. But, if mine is gone, yours can be gone too. Don't panic. I'll think more on it tomorrow.
(1) In the meantime, let's try to straighten your letters out in Advanced Startup. Make sure the Windows partition has the letter C:. And the only other partition that should have a letter there (these days) is the Recovery partition. So, in Advanced Startup...
"Troubleshoot > Advanced Options > Command Prompt"
DiskPart
List Vol
(a) Remove the letters from all the volumes except Gateway & Recovery Tools...
Select Vol=x <<< Select a volume number (not Gateway or Recovery Tools)
Remove Letter=? <<< Remove its letter
(b) If C: is not on Gateway remove the letter it has, & put C: on it instead.
Select Vol=x <<< "x" is the volume number of Gateway
Remove Letter=? <<< "?" is the letter, presuming its not already "C"
Assign Letter=C <<< Give it letter C
(c) May as well remove whatever letter is on Recovery Tools & put R: on it instead.
Select Vol=x <<< "x" is the volume number of Recovery Tools
Remove Letter=? <<< "?" is the letter, presuming its not already "R"
Assign Letter=R <<< Give it letter R
(d) Then Exit DiskPart, exit the Command Prompt, & click "Continue" to get to Windows.
I did that once, & it stuck. Now Advanced Startup always has just those two letters (except the DVD-ROM still gets a letter).
(2) "Well, I was gong to paste in the code"
The clipboard is cleared when you reboot to Windows. So, put it into a file instead. At the Command Prompt in Advanced Startup...
(a) Do a Ctrl-A & Ctrl-C. (Instead of Ctrl-A, you could just drag the cursor over just the text you want.)
(b) Type "Notepad" into the Command Prompt.
Notepad will open in full GUI mode.
(c) Use Ctrl-V to paste into it.
(d) Use the "File menu, Save as" option to save it.
But set a reasonable location in the File Name field. For instance, "C:\Stuff.txt"...
The file will be there when you return to Windows. Open it, & copy the text out.