I'll buy a new USB cable today and try connecting via ADB again. I can't even find the original firmware for this console. It seems like a trivial task to restore build.prop, but it's already driving me crazy. It won't connect via ADB, I can't find the firmware for this device, and it doesn't see the internal memory via Multitool. I'm at a dead end.

I once got the TVBOX to boot into recovery by flashing the raw mmc image directly to a sdcard and then powering on the tvbox with the sdcard

You can backup the mmc using multitool script and on a pc or phone extract the resulting gz file. Then from this raw disk image you need to get the offset and size of the system partition and then use dd to get the system partition out. After that you can make changes to files in the raw partition image and write the whole image back to the same offset. Never tried something like this but if it is possible to get into recovery mode and try if adb over usb is available then editing the system partition would be easier. The first method might worsen things so having the gz file saved at a safe place will be better

The problem is that I wanted to change the fingerprint and changed build.prop. After that, the console boots up, but the launcher does not start. I can only access the settings. And I can't connect to the console to restore the build.prop backup. As I understand it, it is impossible to connect to this console via adb, and multitool also cannot see the internal memory. Are there any options for editing build.prop?

Also, mmcblk2boot0 and mmcblk2boot1 should either have the bootloader or in my case were filled with null bytes. mmcblk2rpmb probably has something to do with TEE OS. Having a backup of mmcblk2 is what that matters