DT4 - Tags hierarchy in the sidebar is not displaying

[BLUEFROG]

Disable Settings > General > Interface > Unify Tags.

Also, did you read this:

READ ME – Running the DEVONthink 4 Beta

Read this if you want to run the DEVONthink 4 Beta… Firstly… Optimally, DEVONthink 4 should be installed on a separate macOS user account in its own ~/Applications directory to isolate it from other user accounts. However, if you want to run DEVONthink 4 and use it with your DEVONthink 3 databases, you need to make sure version 3 can’t be launched. In the Finder, locate the DEVONthink 3 application. Control-click it, and choose Compress… After the ZIP file has been made, delete the DEVONthink…