A VNC client with tight compression support

I need to connect my smartphone to an UltraVNC server and use tight (or ultra) compression for the framebuffers (the target has 4k display, uncompressed framebuffers come super-slowly over WiFi). MultiVNC connects and starts to transfer the framebuffer (i see the new blocks appearing), but does it very slowly. androidVNC connects, then claims to be receiving the first buffer, and gets stuck there (either it takes too long to get the buffer, or it repeatedly fails the transfer under the hood; either way, unlike MultiVNC, it doesn’t even display partial transfers).

Any other options?

FOSS remote desktop clients on Android is sadly as sore spot that could use some development.

You might be able to rig something together with Termux and a local X11 server.