andiedee :
Sorry i should've been more specific!
These are the full names of the SSDs:
Samsung 970 PRO M.2 NVMe SSD 1TB
Samsung 860 PRO 2.5in SATA SSD 512GB
No problem.
https://www.asus.com/us/Motherboards/ROG-MAXIMUS-XI-CODE/specifications/
If using the M.2_1 port for the 970, SATA #2 on the motherboard will be disabled. All the others are usable for the 860 Pro.