Over the course of working on different projects I mistakenly ended up with both Yarn and npm. It was causing me headaches, so I went looking for solutions to convert projects from Yarn to npm. One open-source module I found that has worked great so far is deyarn by MixMax (a B2B SaaS).
npx deyarn and I was good to go.
You can learn more about their journey To Yarn and Back (to npm) Again on their engineering blog where they explain the hows and whys of switching back and forth.
If you have other suggestions, please comment!