It seems like your Java version is out of date.
Using the prebuilt ISO’s is not a failsafe to get the latest build of anything. It is a build from the time the ISO was compiled. made so it is easier to get into MineOS. Much like when you install windows, there is usually updates to install after installing the OS is done. This is why I usually forgo the ISO’s when I install, and go the ubuntu server way, then install the MineOS scripts on top of that. I get a newer install, but also a whole set of new problems, and the option to install things as I like them.
For MineOS this includes udates to the OS, and to requrired system software like Java and NodeJS
Updating java can be done by following this page:
https://wiki.debian.org/JavaPackage
For now you should try only updating java, but at some point you should also update your system:
Most updates can be done by following the instructions on this page:
I’d also like to remind you about this pinned forum post: Basic skills and interests you’ll need to be a MineOS admin
(Oh and if you think getting your minecraft server running puts you in the clear? Mojang currently has this nasty bug that crashes your server if a player is in the wrong area: https://bugs.mojang.com/browse/MC-131071. I have had to manually edit player files to make them start in “spawn” again when they log on since the server autocrashed when he tried to log in while he was in the affected areas. So be prepared for new and facinating ways to be frustrated)