After upgrading to Nextcloud version 10 from 9, creating and syncing files and folders with special characters (space, áéűú etc.) not possible. On version 9 this was not a problem.
Server configuration is Apache 2.4 with ProxyPassMatch to PHP-FPM 5.6.26.
It seems to be working for me. Do you have a specific test case other than, 'áéűú '. Are there any errors in the nextcloud.log file, or the sync client?