Question about Sony UBP-X800M2

MKV (only H264, not H265) and MP4 worked for me via the USB port. Ripping a Blu-ray or something similar will be too "illegal" for Sony, it's hardly supported (even if the legal situation in Switzerland is a bit grey).
You can also play media from a media server over the network. But I have never tested this.

If an external SSD hard drive can be used, it plays MKV with H.264 and H.265 codec, i.e. Full HD and UHD 4K.
In general, it plays almost all formats except DD+ Audio (Dolby Digital +).

Basically yes, especially videos and pictures, as well as music, I haven't tried anything else myself. Simply works via the front USB port.

Si

A USB port (front) is available. For the compatible formats, see technical specifications. As I haven't tried it myself yet, I don't want to provide any "valuable" information. Call Sony, they are very friendly, the technicians are happy to provide information.
Good luck mfg harry

I can't answer that question. It's best to ask sony directly!