When doing a chain and having the latest card resolve, does each player get to react while the chain is resolving during each card is resolving?

Yes, each player has the opportunity to play reactions while a chain is resolving. The chain does not resolve all at once; it resolves one item at a time, and players are given a window of priority between each resolution.

According to Riftbound Rule 340.4 and supported by multiple FAQs (such as FAQ #2952 and FAQ #8375):

The Sequence of Resolution

1. Resolution: The newest (top) item on the chain resolves.
2. Priority Check: Once that item finishes resolving, the game does not immediately resolve the next item on the chain. Instead, the player whose turn it is (or the controller of the next chain item) is given priority.
3. Reaction Window: During this window, both players have the opportunity to play Reaction cards or activate abilities that are legally timed to be played in a "Closed State" (i.e., while a chain exists).
4. Adding to Chain: If a player plays a new reaction, it is added to the top of the existing chain, and the players must pass priority again.
5. Continue: Once both players pass priority without adding anything new to the chain, the next item on the chain resolves, and the process repeats.

Key Things to Remember

• "Closed State": Because there is still at least one item remaining on the chain, the turn remains in a "Closed State." This means you can only play cards or activate abilities that have the Reaction keyword (Rule 309.1.a). Standard Action cards cannot be played during this window.
• Priority Order: After an item resolves, the controller of the next item on the chain gets the first opportunity to play a reaction, followed by the other player.
• Final Link: You cannot react to the resolution of the final link in a chain, as the chain becomes empty and the game returns to an "Open State" (Rule 340.2).

In short: Yes, you have a window to react between every single card or ability on the chain. If you play a reaction during one of these windows, it goes to the top of the chain and will resolve before the items that were previously underneath it.