He is still figuring out the Powerline part. (You can of course always help and try to get it to work on your own. If so then you can base your own firmware on the latest M4R firmware I have linked below.)
If you don't need the Powerline feature then you can always just install the Deco M4R version. The flash layout for all M4R V1 and V2 and P9 V1 and V2 is the same and the hardware is the same apart from the Powerline chip so that is going to work. You just lose the Powerline capabilities with that firmware.
A "how to flash" can be found here: OpenWrt support for TP-Link Deco M4R - #51 by KinteLiX
The telnet enabled stock firmware for the P9 can be found here: https://community.tp-link.com/en/home/forum/topic/175006?page=4
and the most recent M4R firmware can be found here: OpenWrt support for TP-Link Deco M4R - #57 by KinteLiX