Hi! I have a little doubt and would like to ask for your help.
Suppose I have a folder with very many files, can I drag and drop it directly from one database to another?
Is it safe to do so?
I saw on a 2016 thread that the official people recommend exporting it from the old database first and then importing it to the new one.
In 2023, I’m not sure if I still need this tedious step to secure my data.
Looking forward to your response. Thanks! 
Unless you’re using item links to connect documents, I would still advocate the tedious method. It safeguards your data by using the filesystem as a temporary holding tank instead of pushing all the data dynamically through the pasteboard.
Moving items inside DEVONthink doesn’t use the clipboard actually, directly moving is now usually recommended. But checking first that the volume containing the destination database has sufficient disk space (especially if it’s an encrypted database) and that both the source & destination database are verified successfully can’t harm before moving a lot of stuff.
Noted.
Confirming for what it is worth, this week I did some big reorganising of a few databases and simply used the “Move to …” menu to move Groups from one database to the new one. Spot checked that all well and pleased to see all okay.
Thanks for the advice, Jim!
Thank you for your detailed and helpful reply!