The problem is, to find all included (!) paths all paths, including ignored ones must be traversed.
The actual error you get comes from a limitation in the library used for the watching for changes feature: If it encounters any error while setting up watches, it fails, i.e. there is no way to just dismiss errors on ignored paths.
Workarounds: Change permissions such that syncthings user can traverse all folders in your home or disable watching for changes. The ignore patterns are fine.
The error was shown above. But in the mean time I changed the access rights. I hope I won’t get trouble.
The complete error message started with any support information. I don’t know anymore the correct content.