And what do you think I have never shipped a single line of Flutter except having toyed pretty decent apps as side projects? The company that can kill Stadia (had AMD GPUs and servers, had its own hardware controller, bought studios, planning to launch its own titles and what not) can surely kill a mobile SDK for sure without giving it a second thought, like at all.
Only things that should be considered constant at this point are the Google's ad business and everything it gets injected into.
Flutter is open-source though, are you actually worried about Google dropping it and the community being unable to support it?
For context, Killed By Google lists AngularJS, which received updates through 2021, about 5 years after Angular (v2) was released. Polymer is another open-source framework, killed in 2021, and it's still in 'maintenance mode'.
Only things that should be considered constant at this point are the Google's ad business and everything it gets injected into.
Rest is all mortal.