Face ID problem, needing help diagnosing

Hello, I am stumped at this point trying to find the answer on this faceid problem.

I bought this secondhand iPhone 13PM but faceid has been affected first time (having to knock the top camera to get faceid to work) but was repaired by readjusting the lens on the dot projector/flood illuminator. But the problem came back after a few months and basically the Apple repair tech wants me to replace the whole front camera unit for $150… But I wanted a second opinion on this..

Here are what I have found:

• Faceid failed to detect my face but there was no “move higher or lower” message.
• Animoji works okay
• Proximity sensor and auto brightness is normal
• Attention thing does not work
• Flood illuminator and dot projector weak with no dots, compared with my iPhone XS with normal faceid ( see vid for comparison)

• Front camera portrait mode have that yellow text and does show blur and its effects, but when the photos taken are just normal regular ones (no light effects or label as portrait photo in metadata)
• Back camera portrait mode works normally.
• Front camera module is original and not replaced before ( checked with JC Repair software and 3u tools). Flood illuminator, dot projector, infrared sensor are original)
• I have not tried DFU restore, opening up phone if it’s water damaged, or cleaned the dot projector,flood illuminator.

I am not a repair tech but I don’t trust the process some of the local repair person because they are not transparent of what tools they use.