I'm planning a social media mobile app. I would like to prototype using a cross-platform native solution, leaving room for a future web client. In mobile dev, I'm most experienced with Flutter but I use Next.js for web projects. Since I'm not a designer, I think material 3 would be a fair design system and it's integrated into Flutter. React Native does not have material 3 yet but it would allow an easier web implementation (I have found flutter web to be too slow)
What do you suggest?
I think this is a good choice, so many design elements are considered for you such that even if you're not a great designer, as long as you're focused on layout and functionality it's relatively trival to go in later and apply themes and custom widgets. I'm using flutter for the same reasons as you it sounds like and for what it's worth people have been extremely pleased with the tools I've built for them even though I didn't really consider design. Knowing I don't have to worry about making things pretty for them to be attractive to end users is a huge boon for me and I hope it can be for you as well.
RE Flutter Web, I'm sure it will improve with time, I've only ever really seen it slow when it's first starting up. but once the app is "loaded" into the web server so to speak, it's generally been pretty performant assuming I'm doing things like caching appropriately.
Thank you for your response, I appreciate the time you took to reply with certainly useful information.
I got a task at my previous company to compare between Flutter and RN and Xamarin. And Flutter was the better choice among the others, that was before version 3, and now after version 3 it becomes better, so I would recommend Flutter for you.