Having the exact same issue. I’ve had a TCL Roku TV for a couple of years and never been able to fix it, no matter what I try. Outputting stereo audio isn’t an option, as I have a Vizio surround sound system I want to use. TCL and Roku don’t care about this at all and keep releasing TVs with the exact same issue. If I had known this, I would have returned my TV, but I mistakenly thought they’d fix it with a software update.
I have a VIzio 5.1 soundbar system that I use with my P-Series TCL Roku TV and find that the following settings using the Vizio SmartCast app or Vizio Remote give me a pretty good 5.1 audio sync experience using mostly the internal Roku apps (Netflix, Hulu, Prime Video, PBS, etc.) There can still be the occasional drift of audio, but it is mostly if I REW or FWD thru a stream to find a specific time mark. Even when this happens, I find turning OFF the soundbar and back on will create a sync audio experience for the remainder of the stream.Vizio Soundbar Settings using the SmartCast app or Vizio Remote
:EQ = DIRECTTruVolume = OFF
AV Delay = 2 or 3 (Should test each and see if you detect one is better than the other)