Some extras haven't been updated so they may well cause problems.
I had a quick look at TvTagCloud.
Change line 141:
$query .= " WHERE stv.name='".$tvTags."' AND stc.contentid IN (".implode($cIDs,",").") ";
$query .= " WHERE stv.name='".$tvTags."' AND stc.contentid IN (".implode(",",$cIDs).") ";
Regarding PHx, I stopped using it a little while ago in favour of it's built in option.
There are others here who use MultiTV so they may be able to help more than I.
It would be worth updating to the latestcommunity version for php8+ compatibilty. There's been quite the input on getting things working. Always back up your database and files first.