I'll try to summarize my experience to see if it can help someone, as I myself was in a similar situation of frustration and not understanding what was going on.
First I want to clarify why I had to re-install windows 10. That was me on the first day trying to delete the game, and all folders installed that day from the game (Most of the inside windowsapp folder) and then ended up deleting things I needed for some of my apps to run, and they would not work after re-installing them, hence my option was a fresh windows start. be very careful to what you delete inside the windowsapps.
If you don't wont to try anything until there's an official fix, follow most of the tips on link text
after you delete everything on your PC, you might still have less memory in your drive. Right click on it, properties and do a disc clean-up. Also if you have CC cleaner or similar, run it on your registry and fix entries made by the game, since the files are gone it will delete the game entries.
This is what I did after my fresh install of windows 10
downloaded xbox companion app, went to MS store and added the game to a cart, then checkout (for 0$) and then launched the MS store app to install the game. The checkout and add to cart will help to get privileges on the game and I read solves some issues while downloading or trying to install it ( don't go to the store using "get" option)
First time around I installed the game on my SSD C :, which is my main drive for the OS, 500gb, 320gb empty space. everything fine, launched the game and same game guard loading and then nothing happened. I tried the fixes like using powershell as admin and add the lines of code for access, and also tried the privileges on the pso2 folder. Same result after game guard. Uninstall the game, with no problems this time, and no leftover files or space being taken on my drive.
Second time (or more like 5th, but 2nd since fresh windows10) I decided to install the game in my secondary drive, a HDD. It created the same folder, even some in C :, as I explained here link text. Did the powershell admin lines of code, and this time I tried it on both folders pso2_bin, which worked fine, and the oxyna folder directly under windowsapps, not the one under windowsapps>mutable>oxyna. That one didn't let me, powershell kept giving an error saying access was denied. Launcher finishes downloading, Game works!.
cd "D:\Program Files\ModifiableWindowsApps\pso2_bin"
first, then one line at the time
Get-Acl pso2launcher.exe | Set-Acl pso2.exe
Get-Acl edition.txt | Set-Acl otp_notice_na.rtf
Closed the game by mistake, then I couldn't open it again. back to square one.
I opened the launcher again, while it was open, not doing anything, I went ahead and changed the permission manually of the pso2_bin (since I could not do it on the oxyna folder) using the post AccelShift gave, getting ownership of the folder, making sure all the files inside inherit the privileges, then not adding a new permission, but editing 2 existing (second from the top between 2 that have full control, and the user under the one called RESTRICTION) clicked start game and it must have taken 1 or 2 minutes after splash was gone, and the game suddenly started. No errors from there onwards. After start menu, xbox companion window opened and selected my user.
Closed the game, and when trying to launch again, launcher was in JP... and this time wouldn't even get game guard to open. Check files again, while launcher open and done with the check, went to the pso2_bin, did exactly the same thing, and this time I went inside to the notice.txt (opened it and it says NA, but keeps launching in jap, meaning the launcher can't access the file) this time I added myself to the privileges of the notice.txt file. Closed the launcher, opened it again and back to NA, and game was working again.
I'm not saying this will work for everybody, but if you were in a similar place, and have the spare time and try it around, like I did, go ahead, I've seen a lot of people commenting "this doesn't work for me" or " this doesn't help me", well then that comment also doesn't help anyone... maybe your problem is other, go to reddit, there is a mega compilation there if issues and fixes, same in discord. Maybe you can find a solution, or an idea on how to fix it there.