I’ve got an X4 as well, and https://rcarmo.github.io/projects/bun-readlater-epub/ and https://rcarmo.github.io/projects/bun-opds-server/ were created for it.

I have also added an e-ink theme to https://rcarmo.github.io/projects/picoflux/ so I can use the browser on my Nomad instead of my iPad, for those trips where I want to read “live” news but not be suckered in by it (and picoflux is how I deal with title-only feeds as well)