When an app refuses to open, it has usually already started and stopped before drawing a window. From the outside this looks like nothing happening, which makes it feel mysterious. Internally it is a start-up sequence hitting a blocker.
The most common blocker is an instance that is already running. A previous session that failed to close properly holds on to files and ports, and the new launch quietly exits rather than competing. Force quitting the old instance resolves this immediately.
The second is an incomplete update. If a device is shut down or loses storage space midway through installing a new version, the app can be left with a mix of old and new files. Reinstalling or completing the update restores a consistent set.
The third is corrupted local data. Apps store settings and caches, and a damaged file read during start-up stops the process. Clearing the cache is the low-risk version of the fix; a reinstall is the thorough one.