@TP-no-Link This is for V1 and V2 and your Deco M4 is V4 which already support these features since 1.1.0 firmware and your Deco M4 (V4) is already updated.

@David-TP Currently i'm using Deco M4 into AP Mode and all of my devices getting IPV6 from Huawei router but in Router Mode when i turn ON (IPV6) on Bridge Mode so the devices get internet connection...

@NatureX If you are using Fast Roaming you can turn it OFF because sometimes Fast Roaming could'nt work properly because some devices could'nt support Fast Roaming and if you are using iPhones or...

@-Atti Connect your PC to ethernet cable and also Turn OFF Upnp, SIP ALG, Beamforming, Fast Roaming and Ignore Ping From WAN if you are using in Router Mode

@aspaviento Your Deco M9 Plus is V1 not V2 and @David-TP provided you the link of 1.8.1 firmware which is only for V2 and V2.2

@AMKZ You can update your Deco M4 by using Recovery Mode by using your PC or Laptop. https://www.tp-link.com/us/support/faq/2958/