My J3.10.8 site works perfectly in PHP 7.4.3, but when I switch to 8.0.18, I get this error on the calendar web page:
count(): Argument #1 ($value) must be of type Countable|array, int given
And a 500 error in the log. When I unpublish the JEvents - Latest Events Module (3.6.34,April 2022), the page loads fine (minus the calendar, of course).