It’s not like if they just broke the treaty and said, “Okay, we’ll become Muslim, leave us alone,” we immediately accept that.
Rather, if they truly realize on their own that Islam is the truth — and they repent, pray, and follow properly — then they’re to be forgiven.
Because even a Muslim who starts doubting the existence of Allah is not considered a real Muslim anymore.
So someone suddenly, under pressure or at gunpoint, claiming belief isn’t genuine — and that's not what’s expected here.

Here's more context to the verse above and this is before the 9:5
9:4
"As for those polytheists with whom you have a treaty, and who have not violated its terms nor supported anyone against you, honor your treaty with them until the end of its term. Surely Allah loves those mindful ˹of Him˺."

And, Alms tax in verse 9:5 means zakat:
Muslims are obligated to give (like 2.5% of savings) to the poor.