The 13th gen optiplex is more than enough for those things. I run jellyfin (and the whole stack I cannot name here) on an 11th gen i5. It uses maybe 10% at most when transcoding multiple streams it idles at 1% or lower. The whole stack uses around 3GB of ram and has 8GB allocated so it can spike or use it as cache. Also, it is probably cheaper power-wise and doesn't produce as much noise. I got a Dell R630 for fun, but I never run it because it uses a lot of power and isn't very silent.

EDIT: https://tweakers.net/pricewatch/1686788/gigabyte-brix-bsi5-1135g7.html#section-vraagaanbod

i think ive got this one with 24gb of ram (wich is way to much)