Hi Arno,
I upgraded my test site to Joomla 5.0 . jDownloads is one of the few extensions that does not only claim to be J5 compliant. It really is even if I switch off behavior compliance plugin it works like in J4.
There are so many others that do either not have a J4 / J5 version or claim to have one and it fails in J5 native mode.
You did that job well. We Germans normally say "Nicht geschimpft ist gelobt genug" but I feel that a praise is good for our karma.