Thanks for your suggestions. I think having access to my doc wouldn´t be of much use since the structure isn´t there yet. Its basically just simple data arranged a certain way, like in this picture: https://recranet.com/media/EN/planning-board-management/_1440xAUTO_fit_center-center_90_none/33627/reservation-software-planning-board-management.jpg
But this way I learned about NotebookLM, which seems very useful. No fitting result for this specific use case but useful nonetheless.
Conditional formatting does indeed help to make vacant slots more visible. But since its still arranged in a vertical list, its too inefficient for many objects.
One thing that comes very close to a solution would be a kanban widget like this: Release of Ultra Kanban Widget
I already tested it. Basically, each kanban column becomes a time slot and each entry becomes a participant that i can move freely between columns. I can even tag each store for each participant.
Its still not a real booking plan but something we can work with for the time being.