One of my filetypes - the most important one - doesn't want its files to be doubleclicked. I did the needful for checking that the filetype really doesn't work: removed all older versions of my app, redid the launch service database, restarted the computer.
After a lot of staring I can see that I set an UTI identifier for the misbehaving filetype. If I remove the UTI identifier the filetype goes back to working fine.
The docs say:
UTI Identifier (macOS-only)
Required for Mac apps that want to use a file type. The Uniform Type Identifier is a unique identifier used by macOS to identify a file. Following the reverse-DNS format beginning with com.companyName.myTypeName is a simple way to ensure uniqueness. An example of a UTI might be: com.example.contactdata.
So why would the UTI identifier mess up my filetype? Or is there - as usual - something that I missed on this topic?