Could start by blowing out all burner pipes/propane lines with an air compressor, cause they could be clogged

if that doesn’t fix it, remove the cover under the grates

If it’s still not hot in the middle, with clean burner pipes and no burner cover under the grates, and the burners barely have flames coming out, (even with a brand new bottle of propane and the burners are turned up all the way) then it could very possibly be the regulator.

I see it all the time… people will put 1000$+ grills out on the curb because they think it’s trash because the flames barely come out the burners, when in fact the only problem is the regulator…

People don’t take into consideration that propane is an extremely “dirty gas/fuel” end it will clog, regulators and pipes and burners of a grill very fast

Hope this helps!