You have to actively switch on usb midi/audio on your Rytm for it to send audio over USB, can’t remember where you did that but it’s pretty easy to find if you dig around.
As for apps, I usually just record my performances on an app called Audioshare and then “mix and master” with an app called grand finale. This has been my method of recording for ages so it’s nice that my Elektrons can now record directly to my apps without the use of an audio interface