Why did you choose that specific display? A quick Google search shows that driving an e-inkt display can be challenging. Have you checked how hard that particular item is to drive?
Thanks! I can think of so many cool things I would love to build for ~€30,- :)
https://www.aliexpress.com/item/400x300-4-2inch-E-Ink-displa...
I've seen libraries for driving this specific one, so I assumed I can hack it to work. The 800x600 size is perhaps more "useful" but slightly more expensive than something I'd buy without a real need.
Of course people could look directly on the calendar through their phone or computer, but sometimes a quick glance when you're near is all it takes.
There is even a company that has an app that manages that for you, but I forgot what it was called.