Dear Michael,
I tried running the newest TeXmacs on Windows 10 (TeXmacs-1.99.3.9747-win-x86.exe), but it showed me an error - TeXmacs window is very small and I get a system message that "TeXmacsQt Windows has stopped working" (screenshot attached).
However, version TeXmacs-1.99.2.8826-installer.exe works fine. I haven't tried running 1.99.3 on Win8.x, so maybe this error occurs not only on Windows 10.
Error shows up on both of my laptops with Win10, one was a clean install, another was an upgrade from 1.99.2.
Best,
Marcin