I know there are 2 variants of M.2 drive (Sata, and PCIe / NVME), is it correct that only if I get a SATA variant it will disable SATA ports, whereas getting a NVME variant won't?
Yes, usually specified in your manual
Also, does the M.2 port you use have an effect on SATA ports getting disabled or not?
Yes, specified in your manual
Under the specifications (page ix)
The M.2_1 socket shares bandwidth with SATA6G_1, SATA6G_2 ports when using M.2 SATA mode device. Adjust BIOS settings to use SATA device
What that tells you is:
1: M.2_1 (bottom slot) supports both SATA and NVME M.2 drives. However if you use a SATA based device you'll lose SATA ports SATA6G_1 and SATA6G_2 (the top 2 connectors, closes to the motherboards main power connector)
Meaning if you'd insert a SATA based M.2 your windows and steam SSD would "vanish" to the bios (nothing would happen to the actual drives or data itself) But to retain all drives working you'd need to move your windows and steam drive to the last 2 connectors
SATA 1 (windows) > 5, SATA 2 (STEAM) > SATA 6
Now if you insert an NVME drive, you don't need to do any of that. That's IF you u use the primairy slot (to the bottom edge of the board)
M.2_2 only supports NVME drives
Long story short:
M.2 Sata drive in bottom slot > move sata ports 1 & 2 to sata ports 5 & 6 or they'll no longer be accessible to the bios (and since sata 1 is your OS. The system wouldn't boot anymore)
M.2 NVME dirve in bottom slot > all connectors can stay as is > system should just boot up (note you'll likely still need to format the drive in "drive manager" before it'll become available to the OS
M.2 NVME drive in top slot > doesn't affect anything.