My neighbor had a 2020 and it had the rear transmission pump which supplied oil to the front high pressure pump in front of the engine just like the 30 and 40 series tractors.  Which pump was replaced?  I would start with checking oil flow and pressure at the transmission pump to see if it is working.  Has the suction strainer in the bottom of the transmission been checked for clogging?  If the brake linings come apart that screen gets clogged and starves the whole system.