It's not as popular as typescript but not dead, it's consistently active for a decade [0].

Compare it with typescript [1] contributions if you want.

[0] https://github.com/facebook/flow/graphs/contributors

[1] https://github.com/microsoft/TypeScript/graphs/contributors

Don't you find it interesting that node-fetch is slightly less-dead otherwise has exactly the same "aliveness" as typescript [0] from your source (click 5 years)?

[0] https://npmtrends.com/node-fetch-vs-typescript