InfCloud is the last and only functional, standalone, web-based CalDAV frontend currently in existence. It doesn’t really matter how crap it is because there’s no alternative. And besides CalDAV/CardDAV are not exactly rapidly-evolving anymore.

There are a handful of alternative frontends bundled with other webapps, for example Nextcloud includes one, but if you don’t want to install Nextcloud just for that you’re stuck with InfCloud.

I really wish someone would make a modern standalone webapp for this but no luck so far.

Having worked at some point on some calendar interfaces I can appreciate why, because they’re super intricate and difficult.