Warm heat and dash lights

2017 Toyota sr5 v6
Heater blows warm air, Trac off and ck engine light are solid yellow. Water temp gauge only moves a couple of ticks past cold.
Comp code read PO 128.
Checked gas cap, it looks OK. I actually had the check enj light come on a long time ago and gas cap wasn't tight. Coolant res looks OK, nothing wet on pass side floorboard.
Engine runs/idles fine, gas mileage is normal, oil level is normal.
I had a rad flush, trans fluid change, new plugs about 4k ago.
I'm thinking thermostat. I'm thinking the heat I am getting thru vents is heat off block. Other than that I'm kind of at a loss.

 

If the water temp gauge is reading much lower than previously, it may just be the thermostat.
My '06 & current '21 throws a bit of warmer air thru the dash vents no matter what the settings are, even with the fan off (recirc off).

 

Likely thermostat fairly common.

if you do it, make sure to remove the drive belt before removing the thermostat. All the contained coolant spills out and contaminates the belt resulting in a chirping. Especially on an older belt.

 

CT Yankee, Bishop84..
Sounds like solid advice.
I'm a woman and while I can usually diagnose, I'm no good at fixing. I have a guy that works on semis that I coax to occasionally to work on my truck. I'll for sure mention the removal of the drive belt.
The only thing I didn't check was the cabin air filter. I'll do that tomorrow. I change it out every 6 mo and this last time I was shocked at the debris. I don't think that's the prob, but I will check it.
Thanks!!!