I am actually painting a schedule for an upcoming event and the only non-brush design I need are a few rectangles.
These need to be centered to the page but under the 'Arrange Docker' it appears to only work when multiple object are selected.
I'm getting around it by turning on and editing the grid size and using 'snap to' but I would like to learn how to align to canvas.
I struggled finding an answer when researching this, please help

(checked on Linux Ubuntu - Krita 4.2.0-pre-alpha)

Hello,
Here is how I'm able to get vector shapes centred on canvas with the "Arrange" docker:

1. create some shapes in a vector layer
2. use the "Select Shapes Tool" (arrow icon) to select the shapes
3. move to the "Arrange" docker (main menu > "Settings" > "Dockers" > "Arrange")
4. click the center vertically and center horizontally buttons in the "Arrange" docker

I'm not sure about your steps, OS, Krita version though...
Hope it helps!

EDIT: in my case it works with a single shape.