Thanks for the quick response!
I had read through the similar issues here and thought the same thing at first, however the debug log seems to show that the request is getting to the server and that the uncaught exception is in the W3TC hook that handles the ajax request.
I can confirm that this is a fresh install of wordpress, and the only plugin is W3TC. The problem persists.
Could it be a compatibility issue with the wordpress:6.2.2-php8.0-apache image? This should be an easy thing for a developer to check.
The browser network log shows 16 requests to admin-ajax.php after I press the Test Page Cache button, and it is only the sixth request that gets the 500 error.
A “500 Internal Server Error” response code indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.
Examining the request, it seems to be enabling the file_generic test that fails:
_wpnonce=391cb87411
&action=w3tc_config_pgcache
&enable=1
&engine=file_generic
