blast007 was able to build and run the BZ-Next client on a Librem 5, a linux phone with GLES2 support.
Missile Wars 2.3 rendered at around 30fps on the development client.
ImGUI debug UI rendered on the Librem 5.
The framerate is about the same as the regular BZFlag client on this device, with textures and lighting enabled. The client seemed to be GPU bound, so there is room to do more work on the CPU side to ease the burden on the GPU on smaller devices such as these. Some form of culling outside of the GPU might be beneficial here.