Did you read the documentation on Activate:
Activate, Deactivate
These two events are sent to every sub-window of a toplevel when
they change state. In addition to the focus Window, the Macintosh
platform and Windows platforms have a notion of an active window
(which often has but is not required to have the focus). On the
Macintosh, widgets in the active window have a different appearance
than widgets in deactive windows. The Activate event is sent to
all the sub-windows in a toplevel when it changes from being
deactive to active. Likewise, the Deactive event is sent when the
window's state changes from active to deactive. There are no
useful percent substitutions you would make when binding to these
events.
The events are "sent to every sub-window of a toplevel". The wording
literally says "not sent to the toplevel". Dot (.) is a toplevel. So
the docs say that . will not be sent an <Activate> event, which is why
your test did nothing.
Try binding on <Activate> on a sub-window of the dot (.) window. Or
try binding on <FocusIn> or <Enter> events on dot (.).