I use to have the same thing but moved away from the tablet solution and I got myself a pi, and then setup a script to auto start (after boot and auto login) the browser in full screen "kiosk" mode on my home assistant site. I then bought this to attach to it:

https://www.amazon.com/gp/aw/d/B0153R2A9I

I also bought a case for the screen and pi to fit in for a nice visual display (although these days the thing is embedded in my wall), but it looks like the case is now unavailable so might require looking around for one.

If money's not a factor? Maybe a Linux Panel PC.

I've tried a few Lenovos and they seem ok - inc. the Lenovo Thinksmart discussed on the HA forum

All tablets have a quirk somewhere, but FullyKiosk does a good job - if the tablet is any good - so I recommend it. A colleague used something else.. I'll try to find out what it was.

Whatever you do get, if it has a battery, ensure you monitor it's battery and keep it somewhere between ~20% & ~80% with a smart power socket / USB relay

Based on your statement that you've only had this for a few months, my suggestion is to assume you'll want to change it in 1~2 years, so try cheap, named brand, 2nd hand ones from ebay until you get size and rotation right for how you use it.

My dashboard on the kitchen tablet is landscape, but portrait in the lounge (on the ThinkSmart on a coffee table) - both seemed too big initially, now they feel too small.

I picked up on one of these and it’s been pretty solid for the most part https://a.co/d/gaLPokJ I tried fully kiosk but had similar issues to yours so now I just run the home assistant app with a dashboard I created using the wallpanel addon https://github.com/j-a-n/lovelace-wallpanel and am very pleased! If you sprung for a slightly nicer android tablet, your experience would likely be even better

Never tried it myself, but doesn't android come with a built-in kiosk mode? I seem to recall seeing something about that a while back

For the money the Samsung A9+ is tough to beat IMHO.

11 inch touch screen in a slim package. Get a cheap jelly case run a couple screws into the wall, slip the tablet in place, route a charging cable.

No matter what you buy or build it will eventually be obsolete and need to be replaced. A decent tablet will last around 8 to 10 years as a wall mounted dashboard. The A9+ can be found for around 170 right now and the next prime sale will likely see it around 150. So that's around 15 to 20 per year of use and all you need to do is either install the HomeAssistant app or setup Fully Kiosk.

I have 3 Lenovo ThinkSmart View falshed with LineageOS. I've had them for about a year now and haven't had any issues.

Guide for flashing -> https://github.com/pgale/lineage_15.1_Installation_TSV

Never had an mamazon tablet but I guess it has a modified android version like their tv dongle so mostly any "real" android tablet will do, cheapest one would be less reactive but still will works. I had mine on an old Huawei tablet but today I would go for something like Xiaomi pad 6 (don't think it is worth to get a high end tablet for that purpose), whatever you get disable battery saving functionality for kiosk app and you should be good. As for telemetry/spyware, block it at router level so it will be limited to your local network.