Great Weapon Mastery "Immediate" Bonus Action

With the Great Weapon Mastery feat, how does everyone interpret the "immediately" bit for when a kill/critical hit grants an extra attack as a Bonus Action? I've found some old discussions about this but the answers seem to be based on 2014 edition where the wording was different.

If you get a kill/critical hit on your Attack Action, can you move before carrying your extra attack Bonus Action? Normally you'd be free to move before doing a Bonus Action but then you're not really doing the extra attack immediately.

If I've got Extra Attacks, and the first attack I make as part of my Attack Action is a critical hit, then do you immediately take the Bonus Action attack even though it would interrupt the Attack Action? Or complete all the attacks of the Attack Action and then take the Bonus Action attack even though doing it like that means it is no longer immediate?

If an Opportunity Attack gets you a kill/critical hit do you take your extra attack Bonus Action immediately even though it isn't your turn? Or do you have to wait until it is your turn and then you've got to do the Bonus Action immediately if you want to use it?