Hi Andreak,
Yes, this is a known problem,
The JEM Finder Plugin is not unfortunately working (yet) in Joomla 4 and 5.
It has to be rewritten and as we all are volunteers who do this in our spare time, we haven't succeeded to do it.
And at the moment we have only one fully skilled programmer, who can do the more complex task – so we are a bit short of human resources.
If you have programming skills or if you have programmer friends who would contribute for certain smaller sub-projects (like the JEM Finder Plugin) or if you would like to donate so we can also hire coders for such a sub-projects feel free to contribute.