My fanless HTPC has been running for 3 or 4 years now, I based it on the Ryzen 4750G APU (which was a bit hard to get hold of, it is well night identical to the 5700G that had a full market release)...
I like to run my PC's for as long as possible, 10 years not being unusual, as long as it copes with the work it is given.... and streaming, media (video and audio), along with light gaming have been working well. - Over the longer term I find the issues to be the obvious ones.... fans bring in dust and fans tend to fail over the long term (bearings etc...) - and of course, any moving parts involve noise, and being located right next to my speakers, a prime objective is silence!
The APU has a max thermal rating of 65C... - theoretically 65C dissipation should be enough - but actual testing of the CPU shows that if you really try to stress it, the real heat dissipation is more like 95C.
I also wanted a case that would fit into my components rack and be relatively unobtrusive
So I went for the HDplex H5
HDPLEX H5 Enjoys Free Shipping Worldwide Stock Status Asia :In Stock USA :Sold Out ETA Nov 12th Germany : Sold Out
hdplex.com
The whole side is the same sort of heatsink that muscular Class AB (or A) amps often have... and the entire case is beautifully finished.
8 Heatpipes connect the CPU to the heatsink.
The manufacturer claims a TDP of 125C... personally I have found that it tends to max out at around 85C so perhaps the manufacturer is being a little optimistic! - still the end result is a system that under any normal use, including gaming, keeps the CPU below 65C.
Under normal HTPC uses, the CPU tends to idle along in the high 30C's and low 40C's - depending on room temp
It has 32Gb of RAM, lightly overclocked (to optimise GPU performance - through RAM overclock)
It truly is completely silent, containing an SSD, RAM, CPU, and fanless PSU (the PSU is the HDPlex provided unit bolted to the case for cooling ... so no fan there either).
No concerns about noise, no concerns about dust or longevity. (it was built circa 2021... now 3 years old, and no performance issues encountered at this stage)