From what I can see, there's only the one m.2 port. So option one is to go for a 2.5" SSD. Or you can get a PCIe 3.0 x4 adapter like this one So you won't be able to use a PCIe 4.0 NVMe SSD at full speed. It's quite cheap, and NVMe isn't much more expensive than SATA anymore, so I could be worth it.

Just for future reference : M.2 SSD's come in SATA and PCIe. SATA is how the data is handled, m.2 is simply form factor (shape, size and physical connection type.)