Past events disappearing in iMac Calendar app while current events remain visible

Petra01 wrote:

i go into 2025, month and day and add - then it disappears almost immediately

Y0u change the year from 2025 to 2024? That will send it back to 2024 leaving you in 2025.

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and try adding an event in 2025. Reboot normally and try again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

How are you entering the event? Are you going back to 24 to find the month a day to enter it or are you entering it in a 25 day and change the year to 24? If you do that it will disappear from the screen and go back to 2024.

A little detail on your workflow would be very helpful.