3.8 already shipped. Mine downloaded earlier this week.

https://www.reddit.com/r/RemarkableTablet/s/hwLNZX4VTD

A search might be quicker than a question.

For any version after v3.2, the rm2fb framebuffer library doesn’t work, so while you could install toltec, I don’t think there are many use cases, as no end-user apps will work, and nothing is compiled for the newer versions of glibc, etc.