You may use any extensions from MIT, or any free extension so long as you include a note from the extension author that it can be redistributed by MIT as part of the competition.
One of the criteria for the competition is that the project must be built with and open in App Inventor 2 (meaning not Kodular). So, I believe they are referring to all free extensions that are fully compatible with App Inventor.
If your unsure, then ask the developer or test the extension to see if the your project compiles using App Inventor.
As FlailingOctopus mentions, extensions from either community (Kodular or App inventor) may still work with App Inventor. This extension is compatible.
Hi, thank you so much for the extension!
I was wondering if it would be possible in a future update to include two blocks to activate and de-activate the NFC, or if it’s an already available feature (or if it’s impossible to implement it).
Thank you so much again!