When you are entering a gift batch in RE7, a prompt arrives when you add a constituent with a recurring gift that says "this constituent has a recurring gift! Did you want to apply this gift to the recurring?". This same functionality should exist for Proposals (RE7)/ Opportunities (NXT).
If the constituent has an open Proposal with an Asked Amount (even if it doesn't match the amount of the gift), you should receive an automatic prompt to link the gift to the Proposal.
**I have also voted on and agree with the fact that the functionality of linking the gift should exist in NXT, but this functionality should exist in both!**
You can already do this in the database view. You will need to add a User defined business rule for gifts that will give a message when adding a gift for a constituent that has an open proposal. Our BB Designer helped us set it up when we did our database conversion, but you can start with this: https://kb.blackbaud.com/knowledgebase/articles/Article/37507
Agree and would add that we need the options to link to Tributes, Memberships and Events from inside a batch in the web view, just like we can in the database view.