Cool! How can I add a NIP-23 feed?
Feeder v2.8 has been released with native Nostr NIP-23 support: https://github.com/spacecowboy/Feeder/releases/tag/2.8.0

Discussion
nostr:npub1... or nostr:nprofile1... I believe.
This was done by nostr:npub1a3tx8wcrt789skl6gg7rqwj4wey0j53eesr4z6asd4h4jwrd62jq0wkq4k so he should know.
Can we get this on nostr:nprofile1qqs83nn04fezvsu89p8xg7axjwye2u67errat3dx2um725fs7qnrqlgzqtdq0 ?
Yes, exactly as nostr:nprofile1qqsrhuxx8l9ex335q7he0f09aej04zpazpl0ne2cgukyawd24mayt8gprfmhxue69uhhq7tjv9kkjepwve5kzar2v9nzucm0d5hszxmhwden5te0wfjkccte9emk2um5v4exucn5vvhxxmmd9uq3xamnwvaz7tmhda6zuat50phjummwv5hsx7c9z9 just showed, using the nostr URI. You can also use the person's NIP05, or use nostr:nprofile1...
Just type `nostr:` then the npub
Eg: `nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6`