Hi @ThumpieBunnyEve, The Linux dedicated server is not an app that you can use by pressing "play". In order to use the Linux Dedicated Server, you would need to switch to desktop mode, and configure your dedicated server through the text files and launch through command line. https://steamcommunity.com/sharedfiles/filedetails/?l=german&id=360404397
Because the steam deck desktop isn't designed to be used as a regular linux distribution, you may need to do some things like set a password for root, and possibly create a new user with appropriate permissions set.
On the instructions above, you should be able to skip to step 5 because there is a gui.
I wouldn't recommend running a linux dedicated server from a steam deck. We haven't tested the capabilities of the hardware, while theoretically possible, the nature of a battery operated dedicated server and the slower networking speed may not be an ideal candidate. I did find a youtube video detailing the process of turning the steam deck into a home server... https://www.youtube.com/watch?v=6Aey0YFYjbQ
Hopefully this helps.
-Cheebsco