Yes, until the 90s. 

 Hell ya man!  It's one of the greatest scandals of our time!!  They stole real McDonalds from us brother!  https://carnivorebar.com/blogs/carnivore-bar-blog/did-you-know-that-mcdonalds-fries-used-to-be-cooked-in-beef-tallow 

 That’s why the fries tasted better when I was a kid. 

 yes! 

 I think they still used a mixture, this blog says it was tallow and cottonseed oil.

https://krocnews.com/once-beloved-fast-food-items-that-no-longer-exist/

https://image.nostr.build/202742a2817f2f80dc80c296be20fc3d227ac7fca303d9beba4e129cbca3db70.jpg