Huh, what exactly doesn't work? Their own readme says "TruffleRuby runs Rails and is compatible with many gems, including C extensions." (https://github.com/oracle/truffleruby)
That doesn't mean Rails won't run on TruffleRuby. TruffleRuby may not implement 100% of MRI 3.2, but that doesn't mean it doesn't implement all the parts that Rails needs.
https://rubyonrails.org/2024/9/27/this-week-in-rails