Does the Z20 Pro run different firmware than the Z10 Pro? If so...

...what important new features might I be missing with my current Z10 Pro?

 

in terms of the normal features for media playback there isn't a lot of difference, the Z20 pro supports AV1 which is becoming more common online, but it isn't 100% necessary.

you still have good HDR10+ and DV support, still have 12bit colour support, 4:4:4 chroma etc.

The z10 has 2gb of ram, which will make third party apps not perform as well as they could on the z20 with 4gb of ram.
If you are forced to use wifi, the Z20 has Wifi6 vs the Z10's wifi 5, so it could be faster and more stable.

The software is a bit different under the hood, with the Z10 being based on tablet/phone Android, whereas the Z20 is built on Android TV, so again that changes how third party apps work and what is compatible, what you can tweak etc.. but for the core media player functionality it isn't a big deal unless you are running unofficial apps.

that's about it. If I had a Z10 right now i'd keep it for a while and only look at upgrading when the new Amlogic based devices start showing up on the second hand market.