OK, when I open any of my databases (that were originally created by browsing to a convenient place, then right-clicking in the Windows Explorer window, then clicking NEW >> DATABASE) and look at the File >> Options >> General database default location, all of them are pointing to folder Users\<myname>\Documents - which makes perfect sense to me. That is the default path for anything you do that opens a general file in ANY file-oriented utility when operating under your username.
However, it is different if I go to my Desktop shortcut and launch Access that way. From the "Access is open but no file is open yet" panel, if I click Open followed by Browse, it comes up looking in ThisPC\Documents - which I believe is based on an installation default. If I right-click on the Access desktop icon, I can click on "Open File Location" - which is ThisPC\...\Office16.
When I originally installed this package (Office 2021/32-bit), it wanted to know if this was a private or shared install and (I guess out of habit) I listed this non-game software as Shared. "ThisPC" (considered as a folder) is a SYSTEM pseudo-folder. I say "pseudo-folder" because you can't right-click it to open the "Properties" panel. It is like what UNIX calls a "mount point" for a virtual device "point of reference."
This makes me wonder if that default location depends on whether you were running as yourself or as SYSTEM at the time. Which may in turn depend on how you installed Access at the time. Not only "How" but "Where" or "As Whom."