Plywood should be used, rather than luan. Luan is not for floors.

Luan is fine to create a smooth surface for under linoleum. It won’t address any of the problems you mention. Interview more contractors, this isn’t your guy.

Plywood should be used, rather than luan

In this case, luan is plywood.

Luan is not for floors

Luan has been used for underlayment for a very long time.

I’m confused

Discuss with your contractor. Ask them how they will mitigate sounds, and how they will eliminate squeaks. Ask how they will correct the uneven subfloor. Ask why they intend to install luan and how it will help with sound and squeaks.

Thank you! To clarify, he never implied this will stop the squeaking. He is going to reinforce the existing subfloor with screws and replace any that need to be replaced. He wants to add the luan for 2 reasons 1) to create a smooth surface and 2)build up the floor since I’m going from wood to SPC so that we can try and avoid replacing my baseboards.

Make certain that the underlayment used is approved for use under the SPC floors you are installing. All manufacturers will tell you what they allow there floors to be installed over and the level of flatness required. Pay heed to this if you want an actual product warranty.

Says I don’t think nothing, as long as the subfloor is clean and flat. Technically the underlayment is attached (a1.5 mm antibacterial underlayment)

You are not digging close enough in the specs, warranty, and installation instruction. Your subfloors must be flat to 3/16" in 10', have a vapor management system installed, and there must not be any additional cushioned underlay.