ERR_SSL_PROTOCOL_ERROR with IIS 10 and PHP

Question

I have a problem concerning the ERR_SSL_PROTOCOL_ERROR in Chrome. Can anybody help me, or provice some sources, how I can fix that on the serverside?

A quick rundown of the problem:

1. ServerOS is Windwos Server 2019
2. Webserver is IIS 10
3. SSL Certificate has its private key
4. URL Rewrite is configured correctly (I suppose)
5. Port is 443
6. On mobile devices the authentication works but on all others I get the ERR_SSL_PROTOCOL_ERROR error

If you want to help me, I could provice addtional details per pn

THX in advance!