Outlook 2016 doesn't accept password or app password

It was not about the number of core but the processor generation (we are at core 13th generation)

One machine is older - but still 4 cores

I'm running Outlook 365 on two W10 machines and haven't had a single issue, only my Gmail for android (which uses app password) has had the problem.

If yours is working and just giving annoying password prompts then I guess you can just hope it resolves, but I do know they've been phasing out standard passwords for a while now so at some point soon you'll want to move to modern auth with 2FA etc.

Looks like Outlook 2019 now supports modern auth by default, not sure if you installed it before that update if they updated you automatically or if you have to go update the registry. But if you upgrade your account to 2FA and remove/re-add it with modern auth, that should theoretically solve your issues.

Thank you for your hint, but:

1.) I'm running 2 other machines (OL2019/Win10 and OL2021/Win11) with the same account settings (Exchange, no 2FA, no app PW) and never have seen there the password prompt problem.

2.) on above referenced devices (iOS, OL2019/Win11) I experienced also 1 or 2 prompt-less days last week, but now its back.

I'm tired of solving mysterious MS problems by "account optimization trials" and wait until MS will hopefully come up with an explanation one day.

BTW: I still can receive, send and synchronize messages, and I'll continue simply ignoring the PW prompts. ;)

I believe Outlook 2019 still uses old authentication, if you have no 2FA or app password that is probably your problem. It won't totally resolve the problem yet since it doesn't support modern auth (without registry changes at least) but it should get it working a bit better until it is fully resolved.

IOS without 2FA is probably using IMAP, but even if not, you still need to convert to 2FA and use modern authentication.