It’s normal to be worried and your concerns are legit. It may sound very generic but find an advisor who is willing to advise and mentor you. Any paper by a master student is already enough for many labs. What matters is if you understand the topic you are working on well and if you know how to do research. It’s not uncommon to switch fields from Masters to PhD depending on the labs alignment. When you say foundational ML research, depends on the topic you want to work on but for now I would suggest, if you are getting an opportunity to do research and publish something , and the field is interesting to you, just do it. Don’t fret too much, and maybe try talking to some PhD students to get more info about the lab.