Hey there mmVA2023,
We understand you've noticed all day events covering other events on your Calendar app. We'd be happy to provide information about why this is happening.
We've tested on our end and can replicate the behavior in your screenshot when the event is actually not set to an "all-day" event and instead is set from 12 AM to 11:59 PM. Edit the event and make sure to check "all-day". Use these steps to edit events:
Create or modify all-day or multiday events in Calendar on Mac - Apple Support
Create an all-day event
1. In the Calendar app
on your Mac, click Day or Week at the top of the Calendar window.
2. Double-click in the all-day section at the top of the calendar.
To add to the above steps, double-click the event that's blocking the other events to allow you to modify it. Then, press the date of the event and you'll be presented with additional options.
Regards.