What if when you are restarting in safe mode you are waiting for Long time to get to login menu? I’m seeing white wheel in lower middle screen and black curser in upper left hand corner while in start up safe mode sill holding shift key and nothing

"Safe Mode" performs a number of actions including a cursory startup disk directory verification and repair. That can take some time, but it may also be an indication that it has suffered some degree of corruption.

If you have reason to believe your MacBook Air will never start up, force it to shut down by pressing and holding its power button long enough for it to shut down—ten seconds or so. Then, attempt to start it again in the usual manner.

If that doesn't work, then boot macOS Recovery and restore its content from its Time Machine backup.

Should the Shift key be held down until the Apple symbol/progress bar shows, or until the login window shows.

I'm asking because I've constantly read differant opinions over the past ten years or so.

At one time, wasn't the shift key held down until the login window?

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing.

I hold it down until the white progress bar begins to move across the screen.