When using Lefty mode on mobile devices, if you have effects on they can overlap with coordinates.
MCPE-160126
Effects overlap coordinates while using Lefty option
Open
8
(Unassigned)
859578
Confirmed
Multiple
10
effects, lefty, mobile
1.20.40.20 Preview, 1.20.30.22 Preview, 1.20.30.21 Preview, 1.20.30.20 Preview, 1.20.20.23 Preview, ..., 1.20.50.21 Preview, 1.20.40, 1.20.50.23 Preview, 1.20.50.24 Preview, 1.20.41 Hotfix
Retrieved
I don't know too much about UI/GUI or Bedrock Edition, but I think that you are using the "Old/Original" UI/Button layout, which might be the cause of the issue (the issue could also be that your screen size isn't commonly supported). Bedrock Edition also has a screen border setting, but your Hotbar looks normal, so I am assuming it is because you are using the old buttons. But overall, it could be a combination of, screen size, ui scale of 3, and the old ui.
Edit:
Can you try using the new UI and update your post? Thanks 🙂