I would guess it is a problem with OP's account. Which is to say it is thoroughly a Microsoft problem, and probably one that could be fixed but would require weeks of back-and-forth until someone with direct access to some number of auth databases corrected the issue.
I will say, they made a change to the auth system recently that made log-in significantly worse. Now several times a day my session expires or something and I go through a 5-10 second redirect flow which visibly jumps between different login APIs to refresh my log in state. (And of course this happens at the start of the day.)
It's also possible your tenant admin updated Conditional Access rules for some locations or applications. Or maybe they screwed up the Hybrid AAD sync from the on-premise DC. As I've been trying to point out elsewhere, tenant admins have a much higher influence on these outcomes than people are willing to admit, and there are a lot of admins out there who can't be arsed to keep up. I've made some of those mistakes myself.