Select an item in your database and show in Finder. Go to the upper level and you will see the database (unencrypted) inside the encrypted disk image. You can copy it out of the disk image and use it as an unencrypted database.
After copying please close the encrypted database. Then you can open the copied one.
got it - do I need to close the DB in DEVONthink before copying?
No, because closing the database will unmount the encrypted volume. Then you can’t copy 
true - thx!
Right now I return to an unencrypted DB, since my document management is to important to use a unreliable technology!
There is nothing showing the technology is unreliable. This is only occurring in macOS Catalina from the reports here.
To you and to @Nik: Where are the .dtSparse files located - the file path on the machine?
Hi Bluefrog -
the Files are located on my local drive (SSD) in a seperate folder…see screenshot…
…to add…since I have this machine…and was working before…
since I have this machine…and was working before…
Was working before in Catalina… or Mojave?
Was working in Mojave - since Catalina I have the issue…
Yep… as I suspected.
Ugh… but thanks for the corroboration. 
@BLUEFROG, I cannot determine whether the automated unmount happened under Mojave or since Catalina since I just recently switched to encrypted DBs but have noticed the effect just recently.
The DBs are located locally in a regular folder.
We are investigating this and trying to reproduce the issue. Thanks for your patience and understanding.
I have created the encrypted sparsebundle image (APFS) with the disk utility, copied the database in it and changed the suffix to dtSparse. Since then (12 hours) it is not ejected.
If this is accurate, I hope this doesn’t mean Catalina will be unfriendly to HFS volumes. 
Too bad, this morning, the volumes (created with the disk utility) were also ejected …
Good to know. Thanks!
Do you remember whether the volumes are ejected after a certain amount of time after mounting?
That has always been different. Sometimes after a few minutes, sometimes after hours or a day. Even with similar use. However, what struck me today is that both (I currently use only two) encrypted volumes were ejected at the same time. That was probably always the case, because each time the other volumes were no longer mounted, as I noticed this at one. Only the timing of the ejection of the individual volumes was incomprehensible until today …
But I can safely say that other volumes (sparsebundle image) will not be ejected. I have several, which are mounted over weeks.
Do you already use 10.15.1?
Yes.
So far we still couldn’t reproduce this. Does this happen after a certain event (e.g. computer wakes up or will sleep)? Or when other volumes are (un)mounted? DEVONthink unmounts the volume only after closing the database.
