Totally playable, no purchases required.
The gems are only if you want to progress quicker down the research tree by “buying” the tech and unlock the structures faster. But, it’s not required, you can progress normally by producing the required items and sending them to the research lab.
You can also earn “free” gems by watching an ad. Once you have enough gems, you can plant a gem tree (that costs gems) that will produce unlimited gems albeit at a slower rate.
Not sure if this is what you’re looking for, but a Keychron keyboard has a toggle mode for use on Mac and Windows. It has Bluetooth and it can also be used with a wired connection.
I use the K8 model, see below Amazon link. https://a.co/d/d1Oa0Pu