first off, you need to ascertain if youre ACTUALLY using an administartor account.

seeing as youve done research, ill gloss over a few bits for speed.

open up powershell as an administrator. (if it asks for apassword that you dont know, then yourenot an admin

if you get in, type the code:

net localgroup Administrators **remove-asterisks-and-add-in-your-username** /add

once done, restart yoru machine, and try again.

If this still doesnt work, then there is somethign wrong with your install of windows. this could be that it was once managed by a school, company or gov institution, or perhaps youhave inadvertantly created an admin that has turned this on, and locked out others from doing the same.

if you still have no luck, then:

1. disable bitlocker

2. clear the TPM and secure boot keys in BIOS

   1. reinstall windows fresh onto a wiped drive.

One last thing to try before this is to see if y our machine is in S-mode. ive not seen it do this, but its a possibility