Pretty specific usecase, i looked again in the app store byt could not find a widget for a seating representation.
- https://www.seats.io/ => seems like you can embed "interactive floor plan" to your html page and connect with an API to your backend
- you can embed/create a Mendix widget basedn an open source solution; https://github.com/mateuszmarkowski/jQuery-Seat-Charts
- not recommended, but may be useable if you are doing a demo; try to build in Mendix , i think with images of empty/filled seats and list views or template grids in combination with on change microflows, html/css styling, you can come pretty far
If you are able, I would suggest to build a custom Mendix widget based on the open source solution and share it for good will with the community :)
Never done it myself but i think you could also do something with:
https://appstore.home.mendix.com/link/app/105748/ Map marker editor