I'm seeing the same issue, where I can't log into AGOL from Power BI
I've tried the following:
Still cannot log into AGOL.
Existing maps in Power BI do work.
Just can't create new ones.
I have version 2.99.621.0 64-bit (November 2021) on Windows 10 and it doesn't work. I have already deleted the cache, uninstalled, reinstalled... but the same issue; no access to AGOL or AGE sites, just the blank window.
We just identified an issue on the Microsoft side yesterday with the November release and they have a patch for it that will go out very soon, rumored early next week, that will fix this.
It seems that ESRI and Microsoft fixed the issue and it is now possible to log in to AGOL and AGE.
NOTE: I am using the version 2.99.862.0 64-bit (November 2021).