I'm sadly not going to be much help with this. I got the M4R V2 running by scratching my head a lot and looking at the sources of other devices like the Archer C6 V2 and the TL-WA1201 V2 because those use the same chips as the M4R V2. And it was sheer luck that I noticed that the mainboard layout of the V3 looks like that of the M5. Beyond that I've got no clue what's going on and can merely explain why the RGB LED will light up yellow or white.
I would probably go through the post of the M5 and look at the different github links and pullrequest those guys did: IPQ4019: Adding support for TP-Link Deco M5
The pull request from GoliathLabs includes things like these that sound like what you might need:
$(eval $(call generate-ipq-wifi-package,tp-link_deco_m5_eu_v3.0,TP-Link Deco M5 EU v3.0))
ucidef_set_interfaces_lan_wan "eth0" "eth1"
caldata_extract "0:ART" 0x1000 0x2f20
But that's just me tapping in the dark.