Well, that is exactly what i was saying.
Not sure if you got me wrong there but i read it the same as you...thats why i said "why write "one" of them if the meaning is "more" or "all". I was talking about the meaning...there was no intention to replace the word
To your question (and again, how i understand it):
Indeed the only limit stated is that you can replace one attack from the attack action with a shove. If you have more than one action (Haste/Action Surge or similar). You can of course replace one of your attacks from each action with a shove.
As i have stated before the "extra attack" is not an extra action. It means you have an extra attack during your attack action. That is why it is stated as is in the PHB i think because if you choose to use your action for something else than attacking, you cannot attack at all. Even if you have an extra attack.
So in the PHB you could either attack or drink a potion. Not both. You can not replace one of your attacks with drinking a potion or using an object or item. Same with Dashing or dodging.
That part of the 5e rules classifies shove as an attack or part of an attack action. Otherwise you would only be able to shove or attack. Maybe thats why larian made it a BA. It would have to be coded differently than other full actions.
Using the Attack action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them. You can perform one push only per Attack Action
As for this...the last sentence is not needed. The rules states you can replace one attack of your attack action with a shove. Not two, not three, ONE. Why do you have to say it again in an additional sentence?
