Hi mate,
We got the same issue across half a dozen websites after the update to the latest versions of Elementor and Elementor Pro.
Looking at the console it keeps spitting the same 500 error on /admin-ajax.php. Our temporary way to get around this nonsense is to right-click inspect the loading overlay on the Elementor left side and removing the loader from the HTML. Once removed we can make changes to the page normally and save it without issue as well. The 500 error is completely bogus and is an Elementor onload issue that should be resolved ASAP.
Anyways, hope it helps any poor sap out there.