Is this your first print or have you printed successfully before? I had a similar problem - after several perfect prints print quality began to degrade with under-extrusion, first starting at higher layers and only with certain filaments, with some prints still successful, until all prints came out under-extruded.
The problem was that filament residues hat accumulated in the hotend until it was almost fully clogged. Due to the force of the Bambu extruder it was still able to push some filaments through the clogged hotend which made the problem difficult to localize at first. I cleaned the hotend according to the instructions in the troubleshooting wiki and now it prints in perfect quality again.