AFAIK, GrapheneOS supports the Pixel Tablet, which is probably the only truly secure android tablet on the market.

If you're willing to sacrifice some UX, there are some Linux tablets. A cheaper option could be a 2-in-1 chromebook that allows installing Linux.

Otherwise, you could try to degoogle your Samsung tablet by installing LineageOS on it, if it's supported.

The Google Pixel Tab with GrapheneOS. I got the most recently produced tablet that supports Lineage and it's very slow.

The Pixel Tablet with GrapheneOS is the gold standard, but there's even more than just the tablets with LineageOS support if you are adventurous.

I was gifted a Samsung Tab A7 Lite, which is without LineageOS support. However, I've been able to flash TrebleDroid Generic System Images (GSI), which are vanilla AOSP images modified to support as many devices as possible. They come with no Google apps or services.

Nearly everything works as expected, performance is much better, and battery life is unchanged. I can even run Android 15 smoothly when Samsung will end support for my tablet with Android 14. If anyone wants a writeup to the best of my memory, feel free to reply.

What are you using to read comics, and is it available for Linux?

Being that you already have an 8 foot tablet, I assume you're looking for an OS to run on that. The only suggestions I have is possibly LineageOS, if it's compatible. Otherwise you're looking at replacing the hardware.

Is LineageOS available for it? I have a Samsung tablet I reflashed and I've been quite happy with it. Battery life isn't great, but it mostly lives in my bedroom, so not much of a problem.