Could you recommend a good book or online learning resource for Flutter?

Work through the "Get started" section of the official docs[1]. After this you could take a look at Awesome Flutter[2].

If you are more into video tutorials, this one[3] is pretty compact but not made for total beginners.

If you really want to get into it, you could now start checking out a not too big Open Source project like Musify (music player)[4], Localsend (file sharing)[5] or immich (photo sync)[6].

[1]: https://flutter.dev

[2]: https://github.com/Solido/awesome-flutter

[3]: https://www.youtube.com/watch?v=D4nhaszNW4o

[4]: https://github.com/gokadzev/Musify

[5]: https://github.com/localsend/localsend

[6]: https://github.com/immich-app/immich/tree/main/mobile

This is what I went for after deciding against a web stack due to confusion over where even to start with it considering the ridiculous amount of competing frameworks. I also wanted a local first approach and didn't want to maintain a website. Happy with my choice though dart/flutter seem to be universally hated on HN.

Flutter is great for hybrid app development but I am not sold on the web part yet.

That said, there is nothing that tackles iOS, Android and Web very well.