for non-business users, why does OS still matter these days?

I used to be a pure Linux desktop user, for two decades, recently I had to use windows and macos for a few months combined.

In the end, 95% of the time was spent inside a browser, the OS seems non-exist to me for the most part, I now consider myself OS neutral though still prefer Linux when I can choose. Welcome to the cloud era.

I have a bunch of Windows desktops at home that share files using my Windows Onedrive (or LiveDrive or SkyDrive or whatever Microsoft calls it these days - each machine seems to have a different opinion).

What's a good easy-to-use alternative for that in the Linux world?

Ideally it would also allow me to share between my Windows and Linux machines to make transitioning easier.

Syncthing might fit the bill, or just keep using Onedrive: https://github.com/abraunegg/onedrive