Launching a game means that the entire Steam Window fades and it will become entirely unusable until the game starts. That is not a separate startup window, thats just an embedded element inside the main one. If you accidentally click outside, the game startup gets canceled.
It is a bit more than mildly frustrating when Im waiting on the Vulkan shaders for BFV for like half an hour to process.
PCIe (m.2) SSDs are faster than SATA SSDs. M.2 is one way to connect an ssd not the only way.
M.2 is just the connector form factor. Can be NVMe or SATA still.