My case is #2502260040008631. My tech support person was able to reproduce what is going on with the calendar. It looks like they may be working on it because now when you open the calendar although it is still starting with 1899, there is a Today button now that actually takes you to "today".
We are also having issues with Outlook on web calendar when you try to share your calendar using "share calendar". The links are not working for the invitee. I was told although this is related have to create another support case which I am also doing this morning.
I still do not understand the fear/hesitancy of posting this in Service Health (first place I go before researching any M365 issues).
Thanks for this.
In our scenario, the Today button has always worked correcting to Feb 2025. And in Chrome, Edge and Opera, refreshing the page also works correcting to Feb 2025 (in Firefox refreshing doesn't work for us).
Some other observations we found are that agents we have spoken to from Australia and India do not appear to be experiencing this as consistently as we are in North America (in both California and Texas). So it is possible that there may be some regional differences depending on the server we get (changing time zones on the local computer did not change the experience for us).
The agent we are working with today confirmed that they found an internal ticket being tracked for this since February 16. He also confirmed that there is no public link or item in the Service Health area we can reference.
It appears that the issue is now with the development team. No ETA has been provided. We are supposed to get an update on Monday from our support agent. I've also provided the 4 ticket numbers listed in this thread to MS so we can get more visibility.