Like psychoslave suggested, try out mise (https://github.com/jdx/mise). I used asdf for years, did the switch to mise and have never looked back for package management. It supports a huge number of languages and is performant.
I used to use ruby a lot - mostly just because it's the nicest language for scripting things on unix. I can remember trying to get it set up a year or so ago and finding the process difficult (think I was using rvm).
probably good idea to point people here before they install ruby, since it'll compile for minutes then tell you it's missing a dependency, and you have to start the whole process over.
You should be able to do
$ asdf plugin add ruby
$ asdf list all ruby (you'll see 3.4.1, the latest is available)
$ asdf install ruby 3.4.1
And now you can use Ruby 3.4.1 with no issues. Follow that up with
$ gem install bundler
$ gem install rails
$ rails new ...