Certificate Trust Settings - IOS requirements on CA-certificates?

Dear Users,

I'm unable to mark an imported internal CA-certificate as trusted in latest IOS. The certificate does not show up in Certificate Trust Settings, however i was generally able to import and enable it.

Where can i find technical specifications on what IOS requires?

All i found was this article for IOS 13[1] however my certificate fulfills all requirements.

I attach[2] the root-certificate for testing purpose to this post, so it can be tested & analyzed.

Thank you.

[1] Requirements for trusted certificates in iOS 13 and macOS 10.15 - Apple Support (IN)

[2] ***

[Edited by Moderator]