Why change?
The old skool WCAG 2x definition of a web page is not fit for purpose when WCAG is used to test non web user interfaces as it is, for example native apps it leads to suboptimal outcomes. There has been much work done in the past and in the present to define a view for conformance purposes. This effort is currently ongoing as part of W3C Accessibility Guidelines Working Group WCAG 3 work
The current WCAG 3 definition of view
WCAG 3 definition of a view
Testing scope that includes all content visually and programmatically available without a significant change. Conceptually, views correspond to the definition of a web page as used in WCAG 2, but are not restricted to content meeting that definition. For example, a view could be considered a “screen” in a mobile app or a layer of web content, such as a modal dialog.
This definition is all a bit wooly.
Suggested definition
Conformance scope that includes all content visually and programmatically available without a change of context
I have tweaked the WCAG 2.2 definition of change of context and related definitions,
change of context
Major change in the content of the view that, if made without user awareness, can disorient users who are not able to view the entire view [...]