No, there’s no mypaint-like infinite canvas feature. Lukas Tvrdy tried to implement that ten years ago or so, but it is really incompatible with the way our canvas view is implemented. I also had, at one point, the content outside the image bounds showing up dimmed on the canvas background, but the KWord maintainer (Krita was part of KOffice back then) thought that was useless, and killed the feature and made it impossible to reimplement.