How can I downgrade my Deco x20 V4 to the previous version?

To keep it short I've 3 Deco x20 connected by cable running as Router and the unit 2 and 3 are constatly having issues with the connection. this started to happend right after the reboot after the firmware upgrade somewhere last year.

I've tried almost every configuration possible in my network, in other networks, with my ISP router without it, well you name it, i've tested it! The unit 2 and 3 can't simply keep a stable connection.

Also tried to follow the donwgrade (or upgrade) guide from the forum which uses M5 as example, and it doesnt work the units dont get into recovery mode.

With that said would appreciatte any help that can allow me to downgrade the firmware