I have no idea why the extra https// is being added here.
Discourse is running a standard http set up, behind a https proxy that forwards requests from https://community.ist.ac.at to the discourse host machine port 80.
I have the DISCOURSE_HOSTNAME set as community.ist.ac.at
Ok, for some reason its working now. Initially there was an issue with the proxy that was fixed, I think I just posted the emoji before this fix and only refreshed the page after the fix to see if it worked, which it didn’t. After posting a new emoji I found out that the links are working fine.