It is a feature that Guilded had which we used to manage our gaming community before switching to Invision.
Basically, the Bot would automatically post 1 day before (although it would be nice to be able to customise this) with a post like this:
If you click on the reactions on the post, it would automatically sync your response to the Guilded calendar.
So basically, my idea is to mirror that. Have the bot be able to post about events and then have people be able to click on the reactions to then have their RSVP show up in the forum.
Hopefully that explain