The fast Samsung 970 PRO or EVO Plus is a good choice. The Samsung 970 PRO is the best gaming drive card and the Samsung 970 EVO Plus is still among the very best in the PCIe Gen 3 category. Search internet for discounted purchase.
A single OS(C:) boot drive is the most reliable configuration, with the GPT partition format file system to use BIOS boot list option UEFI for fast boot and enhanced security.
The second slot can store a Data drive and can also be used by Macrium Reflect Free to copy (clone) the standby OS(C:) drive that should be part of the disaster Recovery Plan just in case the original OS(C:) boot drive cannot be recovered.
The SATA SSHD drive is very slow, but provides good long term archive data retention. A normal HDD with increased storage capacity is a good replacement. If the laptop is being used when traveling, an external SATA HDD is recommended.