btw.: onboard GPU is build in the CPU
if you're from germany you could use one of the price search engines, maybe this one:
Mainboards heise online Preisvergleich / Deutschland
let say "Intel Sockel 1200"
you're able fine tune the search for the feature you need:
- display ports for your current display equipment
- PCIe slot for your DVB card
- ...?
if you have choosen one:
- check the support, esp. how often the manufactur "tried" to fix the bios issues. in short: how often they released a bios in what time frame. "often" could mean bad (-bios developer). [ my impression: ASUS seems to have some on their payroll since years]
- what is readable on the INet, e.g. linux support, etc.
if you choose a Intel 10000 or 11000 series CPU you need to run nightly !
the i5-11400 (without suffix) CPU is a cheap one, 6 core ....
AFAIK, there no or not much differences to a i5-12400 CPU (maybe I'm wrong)
buy the boxed one; longer warranty
buy i5 versus i3 to maybe use the box as a office/surf box when your TV equipment change some years later
if you want PCIe-4 support for an NVMe check that too (Spec's of the mainboard: what CPU supports PCIe-4 ?)
there are not much differences - apart from the price - between an Samsung EVO Plus (PCIe-3) and an Samsung 980 Pro (PCIe-4)
I'm owning both and the elder Samsung EVO Plus (year 2019, FW: 2B2QEXM7).
The newer EVO seems to have a newer controller and therefore no support for the lastest FW (4B2QEXM7)
If you're looking for a drop in replacement I'd probably hold off till we see Jasper Lake ITX boards from ASRock etc.
Something like the ASRock J5040-ITX would be a good option today, but it doesn't have an M2 port. You can likely get an adapter for the PCIe 1x slot if NVMe is really key to your use case. For LibreELEC NVMe is probably overkill.
Otherwise you'll probably need to go to something like LGA 1200 to get a M2 port, an i3 or low spec CPU would probably suffice.
The RPi4 would be an option too if you're willing to compromise on your Intel requirement, perhaps replace the DVB-S2 tuner with something like a Digibit R1.
what about this board`?
will it be enough to get 4k?
In theory it will do 4K as it’s Gemini Lake, but the Asus website doesn’t confirm it has a HDMI 2.0 port and lists the max resolution as 4k 24hz.
will it be enough to get 4k?
no pcie 
just saying
also J4005 is very low end and already 2018 
J4125 is more recent but its pricewise insane - the market is still a mess
Intel CPUs will be supported as long as Intel continues to upstream and maintain support for them: which is likely, although there is always some delay between latest chip and latest kernel having support. If the old DVB-S card still has the correct slot and drivers in the OS it should continue to work the same old way.
