You can change frame rate to 1/5 in Capture Options in the INDI Control Panel if supported by your camera.

It seems you didn't understand my proposal I want to record locally on SBC (Raspberry/Banana/Odroid etc.) with 30/50/60 fps, and preview it at the same time on a remote PC with, let's say, 5 fps, in order not to overwhelm the network link.

Hi,
Maybe you could use gstreamer for that sort of things. It may be able to save locally in native format using an avi container and in the same time send an mpeg4 encoded stream on the network. That could save your core(s) from overheating as gst will use available hardware acceleration. By the way I wonder if a libav/libgst 3rd-party indi driver would not be an interesting option to handle new high fps cameras. The v4l2 driver may then be kept for experimental use.

Hardware acceleration is good but not always easily available. Can GStreamer use hardware encoding (do not mess with decoding ie playing videos!) on RPi/BPi/Odroid? If yes I will be happy

Solution I proposed is simple and don't need additional tools, which means faster implementation. Also it is necessary to add AVI output support. SER format is inconvenient, Siril can't convert it (you have to process only in it, but I don't want)/cvAstroAlign doesn't support it/Registax opens it but there are garbage frames (from 3 frames only first is OK). Also I couldn't debayer color SER recording.