Hot shrapnel penetrated the port wing fuel tanks igniting the fuel and starting at least one engine fire.
This would cause a fuel tank fire, not a fire in the engine, which would be getting less/no fuel.
There are zero reports about a precrash fire, when there were numerous witnesses. There is also no forensic evidence of a orecrash fire. Both engines landed in a burn area.
6. The left engine, hit by shrapnel reduces thrust output.
The port engine was substantially damaged by shrapnel and would have stopped functioning quite immediately. Broken fan blade sections were found at Rozspyne (the middle of the 3 debris villages). Ingesting these would stop an engne as fast as ingesting birds.
The centre section came down right way up, as indicated by the lower-edge damage to both engines before they parted from the wing. Undercarriage damage also indicates it was at the bottom on impact. The already ripped fuselage roof tore sideways, depositing passengers on the periphery on both sides. There could have been fuel leaking before impact, but would not have burned until the impact provided a spark. This would not have to leave a deep crater.