I think the error might be because the favicon.ico is supposed to be in the public folder, not in the app folder

Try:

1. Moving favicon.ico to public

2. Updating code references. You can just use /'favicon.ico' if its in public

3. Clearing cache/delete dependencies

rm -rf .next _node_modules

I would run a npm cache clean --force for good measure too.

4. Reinstall dependencies -- we nuked them with the rm -rf so need to reinstall

npm install

5. restart with npm run dev