Not the guy, but I used rails at my old job for one and a half year, and used it in some personal projects. I looked into Elixir(and Phoenix) during this time, and Phoenix felt like it was designed for more modern websites, where RoR is built for older and tries to adapt to handle modern ones. It just feels that when you want to do something more responsive in Elixir, it's designed for it, but in Rails, it feels like you're doing something unorthodox or something that is added as an afterthought. Obviously this isn't quite accurate, but it is the vibe I got.

Elixir is also a very cool language in a lot of ways. I wouldn't go all in on Elixir/Phoenix, but that's because there's not a huge demand for it, at least where I reside. I would 100% consider it for some smaller projects though, if I stood between that and Rails, and I wouldn't mind having to get more comfortable with Elixir.

Edit: I haven't used Rails 8, and haven't followed the ecosystem since a bit before, so not sure how this feels nowadays. I *really* enjoy Rails backend though, but the frontend stuff never quite clicked.

Not OP, but I made the move from Ruby/Rails to Elixir years ago, so I'll try to answer from my perspective.

Elixir is a functional programming language based on the "BEAM", the Erlang VM. We'll get back to the BEAM in a moment, but first: the functional programming aspect. That definitely took getting used to. I remember being _very_ confused in the first few weeks. Not because of the syntax (Elixir is quite Ruby-esque) but because of the "flow" of code.

However, when it clicked, it was immediately clear how easy it becomes to write elegant and maintainable code. There is no global state in Elixir, and using macros for meta-programming are generally not encouraged. That means it becomes very easy to reason about a module/function: some data comes in, a function does something with that data, and some data comes out. If you need to do more things to the data, then you chain multiple functions in a "pipe", just like how you chain multiple bash tools on the command line.

The Phoenix framework applies this concept to the web, and it works very well, because if you think about it: a browser opening a web page is just some data coming in (an HTTP GET request), you do something with that data (render a HTML page, fetch something from your database, ...) and you return the result (in this case as an HTTP response). So the flow of a web request, and your controllers in general, becomes very easy to reason about and understand.

Coming back to the BEAM, the Erlang VM was originally written for large scale (as in, country size) telephony systems by Ericsson. The general idea is that everything in the BEAM is a "process", and the BEAM manages processes and their dependencies/relationships for you. So your database connection pool is actually a bunch of BEAM processes. Multi-threading is built-in and doesn't need any setup or configuration. You don't need Redis for caching, you just have a BEAM process that holds some cache in-memory. A websocket connection between a user and your application gets a separate process. Clustering multiple web servers together is built into the BEAM, so you don't need a complex clustering layer.

The nice thing is that Elixir and Phoenix abstract most of this away from you (although it's very easy to work with that lower layer if you want to), but you still get all the benefits of the BEAM.