The problem with the very slow copy/paste behaviour also persists in dark mode. In the standard mode (light and dark = <none>) the copy/past performance is much better (as in previous versions). Is there anything that can be improved?

Hi all - here is another suggestion where I feel I had some improvement in the app's performance:

1. Make a note of all your preference settings that you've modified.
2. Close PL/SQL-D (make sure you're running 64bit)
3. Move all of the "old" preferences to a backup location: your username directory shouldn't be in the Preference folder anymore:
C:\Users\<Your Username>\AppData\Roaming\PLSQL Developer 15\Preferences\<Your Username>
4. Start up PL/SQL-D (it should now start up with the default system preferences)
5. Manually add in your old Preferences or leave it default.

Also remember to do the following:
Disable Clipboard History
Disable Include font style with copy
Under "Object Browser" - ensure that the "Default user selection" is set to CURRENT USER

Another suggestion I see from the previous post, is not to use dark mode - I haven't tried this, but with the above I'm currently running dark mode.