It looks like your UI elements does not scale correctly with different screens.
To solve this you can use the Canvas-Scaler.
Read it for better understanding, but in general, you have to do something like that:
- On your project, select your Canvas.
- Change the UI Scale Mode to
Scale With Screen Size.
- Choose the Reference Resolution to your liking. I also suggest to choose Screen Match Mode of: Match Width
or Height.
- Set the Match slider all the way to either
Width or Height, depends on which one is more important on your game.
From the attached images I feel like your game is based on Height,
but you'll have to see what feels better for you.
The resulting settings should look something like that:
IMAGE (suggested canvas settings)
Now you have to test different extreme aspect-ratios AND different resolutions. Luckily, the editor let you do it via the first tab on the Game screen:
IMAGE (aspect ratio tab)
So you can adjust your canvas settings and specific UI elements accordingly.
If you still have problems with a specific element, check it's Rect-Trunsform settings.
Good luck.