Hello,
I have dietpi 6.30 installed on my raspberrypi4
I have installed Nextloud from software optimised and jellyfin manually. I use nginx as webserver.
I have setup noip and lets encrypt. I am able to access nextcloud from the url https://mydomain.net/nextcloud. But I can’t acces jellyfin.
Following the jellyfin doc, I have to use a reverse proxy : https://jellyfin.org/docs/general/networking/nginx.html. WIth that, I can access jellyfin over the internet but not Nextcloud.
Do you have any idea on how I can access both over the internet?
Thank you in advance ! 
You could use docker for nextcloud, dyndns, jellyfin and nginx proxy manager (use this docker image, its simpler to set up)
Then all services would be properly seperated and with nginx proxy manager you can create a reverse proxy easily.
If you don’t have any experience with docker:
Its extremely cool and you will love it once you understand the concept.
It is normally used via the command line, but there are GUIs available like portainer
Note that it is generally not recommended to have multiple services on the same domain (it is no fun to configure)
You should rather use:
jellyfin.domain.xyz and nextcloud.domain.xyz
and not:
domain.xyz/nextcloud and domain.xyz/jellyfin
Nginx proxy manager uses Lets Encrypt (and renews the certificate automatically)
It may take a while to set everything up like i described it, but it is worth it in my opinion and it makes everything easier if you want to add other services.
Good Luck