I don't know about Flutter, but my issue with these takehomes in a React world is that React is extremely basic. It is only a view renderer, and leaves up to you all difficult questions of: routing, CSS, components, data fetching, state management, even things like how files are organized and named are up to you. As a React candidate, your takehome probably touches on all of these topics, and you (rightfully) probably want to express some kind of proficiency in most/all of these areas. The more senior you are, the more likely you have opinionated ways of doing these things. But in an hour long span, you are left with two uncomfortable options:

1. Write it all yourself. Express those opinions as clearly and bug free as you can. Try to get it all in as much as you can and give up on finishing all the features in the spec. Definitely give up on the UI looking nice -- despite what anyone says, default HTML is not pretty.

2. Use OSS libraries. Are you actively up to date on OSS libraries handling these things? If you're a working React professional, you probably are not, because you're using whatever system your company uses. Do those OSS libraries properly express what you think is good code? And what does it say about you to use those OSS libraries? Do you look like someone who actually understands React and understands those tradeoffs, or do you look like the kind of person that creates the type of React app that HN is always complaining about, one with a billion dependencies?

Sorry if I sound ranty. It's not directed at you. I've just been dealing with a lot of these this week.