I am not a front end developer, but I do understand what you are going through.
You, basically, want to invest in something that is future proof and there are just too many options to evaluate. The pros and cons are fuzzy. You are stuck in analysis paralysis. It is sad to say, this is the case in all branches of software development. Just too many options, but none exactly what you want. For backend, it was first Rails, then Django, Node.js, microservices in Go, now Serverless. Somewhere in the middle, there is also Phoenix, Play, and a dozen other stuff that I have not yet found out.
So, how do you really decide?
First, don't believe anyone who says X is dead. May be X's growth acceleration has slowed down a bit. The existing users are all still there and the community is still thriving as it were.
To arrive at a decision, there are only 3 usecases:
1. You are developing a product that you want to release. Then there is no question. No new tech unless absolutely necessary. Learning a new tech and ability to delivery just don't mix. This is especially true if you are doing this in your spare time as you need to reduce your cognitive overload as much as possible. Usually, the older tech have all their corner cases ironed out and are solid and dependable if nothing else. They also tend to have better documentation and community to help out when stuck.
2. You are looking to develop a new skill that will help you land a better job. Take a job portal that you respect. eg. https://whoishiring.io/ . See which tech has the best offers in your locality and how many companies actually use that tech. That is what you should explore first. Of course, trying as many new tech as possible expands your horizons and makes you as much a valuable hire.
3. Just to have fun. Choose the one you like the most. Build what you like. Throw it away when you get bored. Build again.
All said and done, Flutter from google seems to be growing in popularity, though I do not know how mature it is or even if it truly cross platform yet.
