

There’s this range of Philips signage displays in up to 32" (~$1800 USD): https://www.ppds.com/display-solutions/digital-signage/philips-tableaux
They even run Android, so should be able to install the Home Assistant app natively. Being intended as a signage solution, there’s also PoE (although it is 45W 802.3bt class5), and even room for four 18650 batteries.
Notably though, they use the newer E-Ink “Spectra” (16 bit, 65,536 colour) panel which offers its full 2560x1600 resolution in both greyscale and colour, not the “Kaleido” one (12 bit, 4096 colour) of this Boox monitor that only has half of its 3200x1800 resolution in colour (Boox recommend using 1400x1050).
I don’t know which of the two panels offers better refresh rates, however.
Sadly the one harness my boy hasn’t managed (or indeed, even tried) to escape from was from Amazon.
I’ll leave the link anyway, in the hope you can find something similar: https://www.amazon.com/dp/B0C93LKV5F - sadly it seems to be from one of those fly-by-night brands so I don’t really like your chances.
You definitely want something a bit thicker / padded though, anything that’s just straight straps seems to get wiggled out of. I can see how the dog harness you’ve got (likely designed with a chihuahua in mind, where neck straps have to be avoided) is a bit too much fabric for a cat’s comfort though.
This said, the biggest expression of displeasure I got to the harness was the cats flopping over and pretending their back legs didn’t work.
Once outside mine seems to very much be a “sniffing the flowers” type of cat, just wanders around near the house taking in the new sights and smells, chewing on a bit of grass, etc. Being an indoor cat, even walking on grass seems to be an experience he doesn’t 100% vibe with. At least I’ve not had to retrieve him out of a tree, I guess?
I tried carrying him 20 paces further from the house and he just made his way straight back to safety. Not with the biggest sense of urgency ever seen, but clearly headed back toward the familiar: https://imgur.com/a/PawWQLT
Best of luck in your search.