Was struggling today with the same issue. Link in comment to OP didnt work, but I managed to fix my case myself and here is how I did it for anyone seeking:
1. In my settings for VSCode extension of Maven path to mvn has been as "{DISK}:/{MavenFolder}/bin"
2. I edited it to "{DISK}:/{MavenFolder}/bin/mvn" and everything works fine!

PS: Dont forget to download and unpack maven from official site somewhere