I was playing around with the new RaspberryPi OS version that is based on Debian Bookworm. There is no binary version for TeXmacs out there, so you need to compile yourself.
I had to use the Guile3 TeXmacs2.1 branch from Github, since Guile 1.8 does not compile of this version anymore. Also, there is no Qt4 support anymore. So, I did follow Max guide to compile on Ubuntu 22.04, which works with the notable exception that you need to enable-qtpipes.
Compilation itself worked reasonably fast on my Raspi4 and it will fly on the upcoming Raspi5, I suppose. Starting TeXmacs has a long first load time, since most scheme files are byte compiled and cached, if I understood things correctly. After that TeXmacs is very responsive and works quite well for such a small machine. I also encountered no additional problems under Wayland which is default on RaspberryPi OS, now.