Okay, as a consultant for multiple clients, I have to navigate multiple calendars, because I have accounts in multiple organizations. Keeping availability across three or more calendars is a real PIA, so after years of frustration, I have vibe-coded a small application that syncs the calendars with placeholders. Local only, no connection to outside world. Runs on macOS and it needs to have the calendars in native Calendar.app. If anyone wants to try it, let me know. Will be published after some polishing, but it is kind of working now.