Problem is solved by our developers. I think it was a config problem.
Lastly, Wiki is working with Apache 2.4.46 and PHP 7.4.12.
Unfortunately, they are causing vulnerabilities (we are using "Tenable Nessus" for vuln. scan)
Will wiki release a new version that works with new Apache and PHP ?
Or, can I upgrade Apache and PHP in the Wiki without any compatibility problems?