Strange White/Silver Triangle at the bottom of the screen?

Hello nuredin2018,

Thanks for participating in Apple Support Communities. We understand that you're seeing an unexpected triangle in the Dock under an app on your Mac. Does this only happen under that specific app icon? Also, does restarting your Mac help: Shut down or restart your Mac

Keep us posted.

Cheers.

A google image search suggest that icon is for a focus app. Named Self-Control.

I suspect the triangle under it is telling you it is focusing for you.