FYI - Steam version uses same offline save directory as Bnet version

The Steam version appears to use the same offline save location as the Bnet version. I uninstalled the Bnet D2R and the launcher and installed the Steam D2R Infernal Edition. After I logged into my Bnet account my online chars were synced and my offline chars were pulled from the same directory: C:\Users\[username]\Saved Games\Diablo II Resurrected

Now I haven't tested Steam cloud saving yet but that would be amazing if it worked, too.

If you're on Linux and ran battle.net through heroic games launcher like many, your saves won't automatically transfer since they're in a different spot vs where steam would look. You'll have to find wherever your prefix is for heroic, grab your saves and move them to Steam's prefix location; which defaults to this:

~/.local/share/Steam/steamapps/compatdata/2536520/pfx/drive_c/users/steamuser/Saved Games/Diablo II Resurrected/

They will all be 'expansion' (LOD) chars, there's a button on the bottom right where you can upgrade them. Make sure you transfer all things from the old shared stash to at least one chars inventory before upgrading it and putting them back, they don't automatically transfer over.