itch.io

According to the developers via the Discord server, Soon!

Microsoft Store version is only available for Windows users. The itch.io version is available for Windows, Linux, and MacOS. If you only use a Windows PC, use the Microsoft Store version if it is much cheaper in your region. Updates pop-up doesn't interrupt my experience using the Cider App anyway (itch.io version).

Unfortunately, not now. 

Anytime!

As far as I know, you can only download MacOS's version from itch.io. There is no way to get MacOS's version through Microsoft Store unless Microsoft wants to port their store to MacOS :)

You can request a refund to Microsoft, which will be processed for 2-3 working days. Faster than itch.io's refund.
And you can buy the itch.io version now, with three platforms included for Cider. 

itch.io is better than Microsoft Store's version in my opinion.