@jakeman you gave me a thumbs up but

[nimble hemlock]

I was looking at the Unity releases since 45f1 and didnt see any mention of this bug or its fix

I did see this when googling it https://discussions.unity.com/t/screen-space-overlay-canvas-not-extending-to-edge-of-screen/370020 it describes what i am experiencing exactly with no fix

Should I also show player settings for graphics etc? Although maybe not because if happening in the editor its a deeper problem?

Also here are the settings for the Left UI Panel (left sidebar)

Random thought: maybe the issue is the Panel background image? Maybe because its an image, like a sprite, it does some anti aliasing or something. And maybe I need to use something higher res or maybe I can use a vector based background image.

So removing the background sprite for the UI panel fixed the issue for the left, right and bottom panels. But not the top 🤔

[tribal verge]

you probably have that background sprite on something else as well

[nimble hemlock]

Hrmmm, so actually it seems in the build its not showing the issue on the top bar. Removing the background sprite does seem to fix it. However, if I put the editor in free aspect, it re-appears (only the top bar) and if i switch the editor to 1920x1080 it goes away.