This just happened to me. Last used MSFS2020 about 3 weeks ago with no problems. Shutdown was normal, Today I tried to launch program and got popup showing “Microsoft Flight Simulator can’t open because it cannot be found. The storage device might be missing or disconnected”. Searched everywhere to no avail–No MSFS on computer.
Here’s a thought, I noticed that many of the posts on this subject mention low available space on drive where MSFS is supposed to be stored, same with me–only about 45MB available. Is is possible that MSFS is programed to self delete program if a low available space is detected? I honestly wouldn’t put it past them.