Yes, M4 & M4R are the same. You're using Deco M4 3-pack, right? Did you do a speedtest on the deco app on your phone? If you did, what was the speed there? I'm assuming you enabled ipv6 also from the...

@TP-Link Is this firmware applicable to Deco M4 (US) V2? The deco app doesn't show any updates available, and I don't want to get in problems installing EU firmware in an US router

@Yosea I'm running on firmware 1.5.0 build 20210511 Rel. 34580 & I have the encryption option in the deco app. Maybe it's a firmware issue. You can also check for updates through the web interface...

@xrafaelmuller The web management interface is available...its 192.168.68.1

@dagon The Decos don't have the setting to manually change the channel number

@Yosea Is the deco app on your phone up to date? FYI, the latest version of the app is 2.9.24 (for Android) & 2.9.44 (for iOS)