Shopping for new Intel APU

[TheDreadPirate]

Some options to consider.

1) Just put in an Intel Arc GPU, change nothing else. This would improve transcoding massively. But you must upgrade to Debian 12 and use a BPO kernel (Arc requires kernel 6.2+). THe A310 and A380 have cards that come with half height brackets if your mini-ITX case can't accommodate a full height bracket.
2) If your storage is not locally attached, an Intel N100 based mini PC like the Beelink S12. Super low power, but still has an excellent encoder.
3) Depending on your motherboard, you could also upgrade to a 7000 series Intel CPU, which have HEVC 10-bit support for HDR tone mapping support. You wouldn't need to upgrade the board, memory, etc.

Regardless of your hardware choice, I'd stick with a Debian/Ubuntu based OS. RPM based OSes, like OpenSuse, are not officially supported. RPM packages are community built and usually lag behind official releases. But it sounds like you're using docker, so that limitation may not apply.