I had same problem and fixed, Although it is true that its normal for pc fans to start up at full speed on startup its strange when they dont at first but after an upgrade they run at full speed and stay at full speed
I upgraded my gtx graphics card bought a 3060ti...needed the double 8pin wires from the psu but the back of my pc was a mess so i decided to re wire everything neatly...when i hooked everything bck up i noticed my fans would run at full speed on startup which never did and stay at full speed..took the gpu and placed the old one bck to check if it was the gpu, checked bios to see fan speed settings they were set to standard...checked asus crate app to see the fan setting and was also at standard speed...the asus crate app shows each individual fan current rpm and gives you the header name, cpu fan, chasis fan 1, chasis fan 2 and so on and i noticed that the water pump fan was reading rpms, i dont have water cooled system, i looked online to see the location of water pump fan on asus z590-e motherboard switched to a regular chasis fan connector and fixed the problem now my fans run at normal speed set by the heat motherboard & cpu sensors on startup