If something works on one device but fails on another, you have already eliminated a lot of possibilities. The service may be healthy. The account may be valid. The data may still exist. Now the problem starts to look local.
Turn frustration into comparison
I usually compare four things first: device, network, identity, and application state. Different browser? Different Outlook profile? VPN? Cached credentials? Old client? Same user account?
The goal is not to guess the answer. The goal is to shrink the problem.
Reproduce before rebuilding
It is tempting to reinstall everything. Sometimes that works, but it destroys evidence. A faster long-term habit is to identify the smallest difference between the working setup and the failing one.
That is the real value of “it works on my computer.” You now have a control group.