This is a useful thread. I didn't realise that LineageOS is only minor help for keeping devices updated, and therefore secure.
So, to that end I'm thinking laterally, since I do need to both protect my eyes and get things done without getting digitally robbed by using an outdated device online.
One approach could be to forego integration and go back to displays that are separate to the device. There are eink monitors and eink tablets that can act as monitors. Both of these ruin the ability to be mobile somewhat. Maybe that could be improved.
The only example I can think of an ereader allowing much user control was the Nook ST hacking projects. Joey Castillo's OpenBook is another project like this.
Other news updates:
Hibreak rooted; potentially allows slightly longer updates from Lineage rather than relying on the manufacturer:
https://xdaforums.com/t/bigme-hibrea...phone.4723924/
;joins Hisense A9 series