@magicuf Strange that this works for you!
I reset ETS6, cleared all projects, disabled compatibility mode and tried to import another project, that does not need compatibility but comes from a cracked ETS5 (unsigned).
>>Importing a cracked ETS5 .knxproj with 20 devices does work for me (ETS6N), so its perhaps a ETS6C issue?
I also got the license error when trying to import the unsigned project to ETS6N.
Then I imported a signed project from a licensed ETS5 -> no error here
Then I tried to export the same signed project from ETS6N and got the same “This project cannot be exported with the licenses installed” error.
So ETS6N and ETS6C behave exactly the same for me.
Then I created a fresh new project, added 5 devices and was able to export the project. After adding another device (6) I got the error on export again. So ETS6 is checking the demo devices count.