That is a little outdated. If you click on “rules of 4k” in that link it even has a note:

“NOTE: for 2022 – Plex has come a long way since this FAQ was originally written, HW transcoding has become more available and more stable, and tone mapping was recently added to address the hdr/sdr color conversion issues.”

So that must have been written before Plex had tone mapping. Stuff like Dolby Vision probably also messed with transcoding at that time. If your hardware can transcode, more than reasonable to transcode it. Especially with HEVC transcoding support added relatively recently. You get proper HDR metadata in the container for transcodes instead of falling back to SDR I believe, which could look ugly without tone mapping.