Most people using Gen4 NVMe SSDs don't need to worry about it ...
The Raspberry Pi 5 is the first single-board computer from Raspberry Pi to feature support for PCIe add-ons like M.2 SSDs. But since there’s no M.2 slot on the board itself you need an adaptor board ...
The TerraMaster D1 SSD Pro outdid the mighty OWC 1M2 80Gbps in synthetic tests, and came close in real-world tests.