This is a helpful addition and would work for some use-cases. For me, as a person using multiple Discourses and therefore heavily invested in Discourses, I could subscribe to their calendars and have a single up-to-date place where it’s all together.
However, the use-case that prompted the OP feature request was a conversation that initially took place completely on openhealthhub.org via Private Message wherein I arranged a date and time to meet by video call with some potential Wiki contributors (these are not Discourse-invested people who will use the Calendar URL feature), and then we had to fall back to email for the final part - the calendar invite for the call.
It’s low-level friction on the simple stuff, like this, that drives even quite engaged Discourse user communities back to email, Teams/Outlook, and other platforms. Discourse as a work platform would be a great fit but without proper calendar invites it kind of falls flat. As a person who is often trying to pitch Discourse to unbelievers, this is when I can almost hear their brains clanging shut.