Try removing the registry as suggested by Hans Lu MSFT:
How to uninstall & remove Skype for Business from registry
-----------------------------
If this is helpful please accept answer.
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So I used to have Skype for Business on my laptop. It came already on it so I never really used it for anything. Recently, it started to show the loading screen for it but never went away. I've tried to restart my laptop, I've hard reset it, and I've even uninstalled the app. But it is still there, stuck on the loading screen. I'm not sure what else to do to get rid of it.
Try removing the registry as suggested by Hans Lu MSFT:
How to uninstall & remove Skype for Business from registry
-----------------------------
If this is helpful please accept answer.