A UI like a calendar has been iterated on enough by now that it doesn't really need reinvention. Google, Apple, Outlook and the rest all look largely the same for this reason.

I wish more people would do this! Imitation is the sincerest form of flattery and all that, sure, but especially with UI/UX, gosh... just give your users some time-proven patterns that work well, developed by giant companies who have more UX people than you have employees. No need to constantly reinvent the wheel only to deliver some stylish thing with terrible usability...

Oftentimes I wish the Web had built-in UI primitives like this, the way we do for a checkbox or text field, so that websites aren't constantly trying to reinvent basic widgets. Bootstrap, MUI, Tailwind components, etc. kinda do that, but they're not really standard.

A quote that is often helpful in product design: "Good artists copy, great artists steal."