1. Yes, the BIOS allows the manufacturer to set the point where the processor throttles (cTDP). For the 5800u, cTDP can be set to between 10 and 25 watts:
https://www.amd.com/en/products/apu/amd-ryzen-7-5800u
Looks to me like you left cTDP at the default, 15w. I say this because, throttled...