Asklemmy

You probably want to use a regional instance to have more relevant users, groups and events, but there is a global search engine for Mobilizon

For example, I am using a Polish instance, with an unsuprising domain https://mobilizon.pl

With an account, you are able to publish events, with header image, title, category, tags, date, place, description (with formatting available), and metadata. The event can be accesible publicly, or only via link.
The event (if public) can federate (and be boosted to e.g. Mastodon) and be commented, but you are able to turn off the comments.

Individual account can only be followed from Friendica, but not from Mastodon.

For more features you want to create a group. A group can be followed from Friendica and Mastodon, but only Mobilizon accounts can become its members. Group members are able to participate in discussions (not visible from outside), manage a "common resource folder" - links, make group events and group announcements

You can experiment with Mobilizon features with a demo instance