During setup
The last screen of setup says You’re all set and offers three tick boxes, all ticked to start with.
Untick the first one and nothing changes about your current default. You can
come back to it whenever you like.
Later, from Settings
OpenSettings > General. If Ve is not the default, a banner sits at the top of
the page reading “Ve works best as your default browser” with a Set as
default button. Once Ve is the default the banner is gone. There is no
separate toggle.
Later, from a new tab
The same offer appears as a strip on the new tab page, with a × to dismiss it. Dismissing hides it for five minutes, after which it returns if Ve is still not the default. Once Ve is the default it stops appearing.What macOS does
Pressing Set as default does not flip anything on its own. macOS puts up its own confirmation dialog, and the change happens when you answer it.
Ve keeps checking in the background while the dialog is up, so the banner clears
itself once you confirm. You do not need to reload the page.
To switch back, set the other browser as your default from that browser, or
from System Settings.