I would really advise against investing in flutter.

It's "kitchen-sink" approach is resource-intensive to maintain. E.g., there's a language to maintain and a full suite of controls (doubly hard since integration with OS UX conventions is a constantly moving target) in addition to everything else you need for a full cross-platform app development platform.

Yet, where's the revenue stream to pay for it?

I think it's a matter of time before Goggle pulls resources off it.

It's open I believe, so it won't just stop, but it will quickly sink into disrepair without significant resources maintaining it.