I wonder why there is no way of using m'y own certificates. As far as I understand gmnisrv imposes to create its own certificates by himself.
I'm not confortable with it.
This is by design. gmnisrv manages certificates entirely for you for use with TOFU. The sysadmin should never concern itself with certificates. Ask yourself if you feel similarly about your SSH host keys.
My SSH host keys concerns only myself, my website certificate concerns everybody. I do not understand this choice.
Gemini does not use the global CA system, even though it uses TLS for encryption. It is a TOFU system. This is still WONT_FIX.