If you don't want a source event to be blocked on your destination calendar, simply add the #nosync hashtag to the Description field of the source event.

Here's an example of what that would looks like in practice:

Note: Others might be able to see the #nosync  in the Description field if they have access to viewing details about your source calendar.

If you use an "out of office" event in Google Calendar, there is no description field. In this case, add the #nosync hashtag on the title instead.