My part-list writes:
I was wondering, what consequences does it have for my build performance-wise, AND is it something that I should pay attention to when building the pc??
Part list: https://se.pcpartpicker.com/list/RWGhzY
You have nothing to worry about as this is normal.
The M.2 SSD shares the same lanes as one/two SATA ports which will be disabled. Since you have 6 SATA ports in total, that leaves you with 4/5 SATA ports to add additional SATA devices.
You don't need to do anything, just plug in the M.2 SSD and check the motherboard manual to identify which SATA ports are disabled and avoid them.