As the title says, I have the 15.1 beta on my M1 Macbook Air, and I don't have Apple Intellegence in my settings and no prompts to join the waitlist, etc. I had no issues on my iPhone or Ipad Pro.
Where are you geographically? If in europe, officially you are out f luck at the moment. Potentially with some effort you can get on the waiting list, but there is currently no works-4-all-on-any-device-approach.