Confused about upgrade

We have Go5G Plus and two Samsung S24 ultras that are now paid off.

We'd prefer to trade in at the Apple store to get unlocked phones since we plan to spend the summer with family in South America. Their website is showing we'd only get trade in credit and nothing from our T-Mobile plan for monthly promo credits. Is that true?

if we do it at the T-Mobile store, would they switch our plan since they changed the plans?