As others are pointing out, CouchDB may not be a bad choice but it's probably more cumbersome than necessary. Phoenix/Elixir are great and I use them at work every day. The default assumption in Phoenix is a Postgres database and the data mapper Ecto works really well with Postgres. If you use fly.io or render.com for web app hosting, they both have super easy guides for Elixir/Phoenix + Postgres.
REST might be easier to get up and running with too, because Phoenix does it out of the box. You could then move to GraphQL iteratively once you have your core logic in place and the Flutter app working.
Overall I think you find Elixir refreshing coming from a language like C++. The tools all work pretty well and are easy to learn. The REPL is nice. The package manager is world class. Testing is built into the language. The developer experience is just really great.
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As others are pointing out, CouchDB may not be a bad choice but it's probably more cumbersome than necessary. Phoenix/Elixir are great and I use them at work every day. The default assumption in Phoenix is a Postgres database and the data mapper Ecto works really well with Postgres. If you use fly.io or render.com for web app hosting, they both have super easy guides for Elixir/Phoenix + Postgres.
REST might be easier to get up and running with too, because Phoenix does it out of the box. You could then move to GraphQL iteratively once you have your core logic in place and the Flutter app working.
Overall I think you find Elixir refreshing coming from a language like C++. The tools all work pretty well and are easy to learn. The REPL is nice. The package manager is world class. Testing is built into the language. The developer experience is just really great.