That's what I've been curious about, but even still on a DSM 223 & 418 I've found them alright to an extent running Radarr/Sonarr/Transmission.
I did however run into problems trying to use them via Container Manager aka Docker on the DSM's.
Jellyfin thou is definitely best run on something that can transcode media and the DSM's are definitely not cut out for that, and if your Windows PC has an Intel processor will see you having less issues. Good luck you ;)
Just had a nosey, that DSM 923 (Vs 423) doesn't have a discreet GPU.
What rules are you putting on your downloads from the arrr's, and do you find some struggle to transcode w/ Jellyfin?
I've had to lower the rules since it got silly trying to transcode 80GB+ files over the puny specs of the DSMs > N100 SFF box I'm testing with, and use them solely for NAS / arrrrrs. I still need to invest a little more I think :/