For everyone who has error BLZBNTAGT00000841 and or BLZBNTAG with different endings
If you have the same issue I had where Battle.net says that you need to login as a admin to do anything.
From what I found this is what worked for me:
1: Delete Battle.net and also every folders in programm files in %APPDATA% , %TEMP% delete everything with the name battle.net and or blizzard.
2: Restart your computer
3: Go to my pc right click on the hard drive or ssd go to tools and do error check this takes about 20 min.
4: Update all you drivers
5: Restart your pc again
6: Disconnect from vpn´s and or conncet to another internet connection.
7: Now everything should be clean , now reinstall battle.net
8: (Optional) Open Battle.net as adminstrator
9: should work fine now
BUT if it still doesnt work uninstall all your games on bnet and all document folders of that games close addon programms such as curseforge and than repeat everything .
10: if still doesnt work than you should try doing everything but also disabling your anti virus , updating windows.
dont know how this error happens but worked for me after trying to fix in hours.