Ooh. Finally something I know a good deal about.

I’m a mastering engineer and sync files with folks all over the world.

I have been using this really great app for the past few years: SAMPLY

https://samply.app/ Let’s all collaborators upload files and comments by timestamp are excellent. Works on a potato.

Also, for general big file swaps, The 2 most easily obtained by the majority of people in my experience are Dropbox and Google drive.