Hi Ivan,
Next thing I'd try would be a wireless charger. You can pick up an inexpensive one just to test the charging. If it works, that would tend to eliminate the charging circuitry on the motherboard and the battery as sources of the problem and instead point to the charging port flex cable assembly as the likely culprit.
[guide|129914|iPhone 11 Pro Max Lightning Connector Assembly Replacement - iFixit Repair Guide|new_window=true]