You could also (hard) limit the total (virtual) memory process will use (but the system will hard kill it if tries to get more) with this: systemd-run --user --scope -p MemoryMax=8G -p MemorySwapMax=0 prismlauncher
You would have to experiment with how much Gs you want to specify as max so that it does not get outright killed. If you remove MemorySwapMax the system will not kill the process but will start aggressively swapping the processes’ memory, so if you do have a swap it will work (an depending on how slow the disk of the swap is, start lagging).
In my case I have a small swap partition on an m2 disk (which might not be recommended?) so I didn’t notice any lagging or stutters once it overflow the max memory.
So in theory, if you are memory starved and have swap on a fast disk, you could instead use MemoryHigh flag to create a limit from where systemd will start the swapping without any of the OOM killing (or use both, Max has to be higher then High obv).