what can you put in a pcie slot

If you have a dual SIM variant, you can either put a second SIM or a memory card into slot 2. If you have a single SIM variant, you can only put a memory card into slot 2.

However, some computers, especially laptops, have only one PCIe slot that can connect NVMe SSD. What to do in such a situation?

What Does a PCIe x16 Slot Look Like? ... However, since PCIe slots are cross-compatible, you can install smaller x4 cards, like an NVMe SSD expansion card, into the bottom x16(x4) slot instead.