I discovered another small anomaly when upgrading a site from 7.4 to 8.2 with PowerCMS installed, but I didn't have the same issue on other sites so not sure why I did with this one!
After upgrading, the URL for the CMS stopped working (blank screen). I had to change the following on line 14 in the admin_cms/common/installed.php file:
Original:
$installdate = abs2rel(rel2abs("../Connections/installed_cms.txt",dirname(__FILE__)),getcwd());
New:
$installdate = abs2rel(rel2abs("../../Connections/installed_cms.txt",dirname(__FILE__)),getcwd());
Not sure why PHP8 would think the file is located one level further up, but there you go! :-)