There aren't any functional Digic 7 ports yet, so making one for M5 requires original reverse engineering and development by someone with the camera and the relevant skill set.
Some significant progress has been made since the 2017 post you quoted:
M100
https://chdk.setepontos.com/d/13943
G7X II
https://chdk.setepontos.com/d/13773
Ghidra provides a good, free reverse engineering environment
https://chdk.fandom.com/wiki/Firmware_analysis_with_Ghidra
