Synchronization error for Nextcloud Desktop Client

Eventually this error happens with some files, would it be any restrictions for executable files?

503 is a internal server error. So your webserver logs should help you. You can restrict the file types with the files-access-control app but it is also possible that this is implemented on the webserver directly.

Thank you very much for the answer, it already gave me a way, I will check.

maybe those threads are connected?

This problem is solved :
Synchronization error for Nextcloud Desktop Client

Porém este continua :

Windows 10 Synchronization indication of folders and files are gone