I'm pleased with OBOOK5. It runs Obook OS which is a Linux OS. Never nagged me to connect to WiFi or anything, I simply plugged a cable to transfer my local stuff.
Also hearing good things about XTEINK X4.
I’ve had a pair of Nook Simple Touch for over ten years and they are wonderful for PDFs. Stored 100% offline. Good for prepper books.
I have an XTEINK X4. It's quite small, but if that's ok with you, then it's a fantastic little reader.