Divoom devices have firmware.
I have looked into it a bit, but I've not done anything interesting.
It is likely possible to dump the flash via UART or something, but update files are available too.
Some devices have firmware flashing kits.
Nowadays, all updates are delivered through the app OTA.
These show the full firmware, NAND layout, and instructions on how to flash via USB. Very useful.
I will not be uploading these, but here is a list of devices known to be compatible.