[benwaggoner]

This is all HDR? HDR and SDR need a variety of different parameters.

At CRF 16-18 most things should look pretty good, so it's more a matter of tuning for encoding speed and file size.

deblock=-1,-1 is much less needed in x265 than x264.
--ctu 32 is a good default for live action
--hdr10-opt is pretty essential for HDR-10 encoding
The more grain, the higher --psy-rd, --psy-rdoq, --nr-intra and --nr-inter values you'll want to use. --rd 4 can outperform --rd 6 with high grain as well.

--rskip 2 is better than the default mode.

For animation, I like to use --tskip, --tskip-fast, --tu-intra-depth 4, --tu-inter-depth 4

--csv-log-level 2 can be great for advanced users in diagnosing quality issues.

Do NOT use --tune grain, which is horribly old and terrible.

Assuming you are doing SDR and HDR across 8 genres, that's 16 different parameter sets. If you want more than just general advice, you should do some test runs, then share your command lines and more specific questions.

I have no idea what counts as a "low luminance film" - can you give an example?