Experience designer here. Flip your question around. Ask people about what they hate about event planning, RSVPing, meetups, etc. Then fix one of those things.

Find a user need, the build something to address that need.

"Help me with my homework"

Pro tip: if you want to ask for help, it's not a good idea to disparage the people who are supposed to help you immediately before you ask for help

For programming, you should probably be able to copy that project design.

If you want to make it difficult for yourself, you pick a user or use case to optimise for.

Maybe you make it a wargaming centered booking and matching site (for ladders and weekly games type tournaments)?

Maybe you make it conference centre based, giving appropriately sized suggestions and showcase the rooms?

Maybe you make it for yourself and add schedule sync, or notifications, or whatever you've always been missing from your calendar app.

Why event organization? are you already familiar with each piece in that list? Why that tech stack? Do you need to care about scaling or is self hosting more fun for this?

The distinct concept might be to take that stack and do something else with scheduling? I think weaving in a thing you like or want to specialize in would be better than a generic scheduling app (I don't know those apps you mentioned).

If you're doing a web app focus then the MongoDB INSERTS and updates will be easy to template once you find how they communicate. The DB should do less of the logic and just hold your "primative" data that can't be calculated. It might even do BLOBs if you want to skip a cloud bucket because you won't have to scale..

Good luck!