The processor has a default memory speed specification, which you are correct for a 7535HS it is DDR5-4800. However the motherboard BIOS can control what speed the memory runs at, and may have the option to use XMP/EXPO memory profiles. Unfortunately many laptop BIOS do not allow adjusting memory speed, unless it is a gaming class laptop.
As to why MSI would put DDR5-5600 memory in a laptop that will only support DDR5-4800 speed well that is a question you'll have to ask MSI support.
Ryzen R7 5700X | B550 Gaming X | 2x16GB G.Skill 3600 | Radeon RX 7900XT
Ryzen R7 5700G | B550 Gaming X | 2x8GB G.Skill 4000 | Radeon Vega 8 IGP
Ryzen R5 5600 | B550 Gaming Edge | 4x8GB G.Skill 3600 | Radeon RX 6800XT