SOLVED: Jellyfin dashboard not saving https enabled checkbox

[Peval]

Dear Community,
I have Jellyfin 10.10.5 running on my Synology NAS.
In the dashboard settings, http is enabled on default port 8096 and I would like to enable https on a custom port 8443
I can tick the https checkbox and change the port number as you can see here:



Then i click ok at the bottom of the page, and i get the following warning message:



I am using Tailscale and I already have a valid certificate for the URL of my NAS, so I assume there is nothing I have to do here in the dashboard and everything should be saved and fine
However if i reload the page, or i just exit and come back, no settings have been saved and i find the page as it was with no https enabled as you can see here:



Same result happen even if i try to enable https keeping the suggested port 8920 or any other port.
What should I do to enable https?

Many thanks!
Paolo