Tockify supports user-created events, and you can embed their calendar on your site. It's another subscription per calendar so it adds up if you need multiple calendars (right now it's $8 per calendar per month).
Tockify has a lot of the features folks have been asking Squarespace to add for years, like calendar sync to Google calendars, lots of visual customizations without code, and repeating events.
I haven't found any other calendar that can do all of this. (I'm not affiliated with Tockify in any way.)