[Quoth]

The app worked after the update, but the ebook pages were all blank.

Boyue Likebook Mars with Android 8.something. The EXACT same Android on a phone continued to work.

It's a nice Eink Android. The Native app is a bit like KOReader, which works.

The fact is that if you buy an Android eink for other than the native apps, you might be wasting €200 to €500. No-one can guarantee the app you want will keep working.

I've had 8 makes of ereaders (well, the reMarkable isn't really an ereader). I've had/have 7 different (distinct) Kobo models, 3 different Sony, 6 different Kindles.

I've read the threads on Android eink models.

I've built two prototype LCD VOIP 4G tablets running Debian.

I've Palm PDA with ebook reader.

I've got working Androids from 3 to 14.

Library or Subscription applications
The issue with those is you can't stay on the old working version as soon it stops connecting to the local lending library, or KU or whatever.

Bought ebooks
Remove the DRM and backup and likely it doesn't matter if it's a dedicated Linux ereader (likely more stable, better battery life) or an eink Android tablet. You'll be able to use it till the HW wears out. True for my Gen 2 and Gen 3 Kindles which still actually work with Amazon (there is GSM EDGE still for the Gen 2, though 3G is gone, why Amazon still supports it – at least May 2025 – is a mystery).

Loads of Kindle App versions don't work now with Amazaon to buy or borrow, but all Gen3 & later ereaders still do.

EDIT
LiChess, K9 mail sort of work on the Boyue Mars. Most medial players have broken interfaces. Never found a Solitare that worked.
I considered an Onyx Boox, but you can buy a decent Kobo and a real tablet for the same price as some of them. I saw the 10" Color Boox in real life and it was garbage compared to the NxtPaper 11. The Nxtpaper 14 is cheaper than a secondhand one.