JEYI's new PCIe to M.2 adapter is flat and sits flush with the motherboard when installed in a PCIe slot. It basically takes up no perpendicular space, allowing an SSD to be installed even in tight spaces where the GPU is often blocking the area. The adapter features PCIe 4.0 speeds and is backwards compatible with PCIe 3.0 as well.

You can use Xbox Expansion Cards on PC with a CFexpress adapter since these cards use a standard CFexpress Type-B connector. There are various options available such as PCIe to CFexpress or M.2 to CFexpress, and all of them are inexpensive. You just need to format the Expansion Card before it's useable, but don't expect blazing-fast speeds afterward.