I bet they will just recommend some temp work arounds, instead of replacing the Engine for free under warranty. Once all engine warranty is expired. Dealer / Toyota will say Engine has to be replaced and you pay full price. I spent several hours in this forum, there are several issues related. I recommend launching complaint at NHTSA saying defective engine. more complaints they get possible recall of Gen4 for Head gasket.
It is sounding like coolant leak , P148F from TSB - T-SB-0135-19 clearly saying it is Terminal illness of Engine. They are just trying to give some medicines to let warranty expire so that they can escape.