I’ve long forgotten about the feature since it first rolled out in 2020 as a way to curate recommendations — but now it’s going away. Developer Alessandro Paluzzi first spotted the change, which Instagram spokesperson Mari Melguizo later confirmed to The Verge, saying Guides will be transferred into private saved collections:

We are sunsetting the Guides feature and are converting all existing guides into private saved collections. Usage is low and we are always looking at ways to simplify the app. People can access their saved collections via ‘Saved’ in the profiles settings tab.