@Sybe thank you for your response, however none of it was at all helpful with the issue I was having. Please refrain from referring other users to the guide from 7 years ago, as it is quite out of date - the Google Calendar UI has completely changed, and the built in "How to find the calendar address" within the Import Calendar menu in the listing is easier to follow and more up to date.
For the reference of anyone who has this issue in the future, Google Workspace only shares free / busy calendar information to users outside the organization by default, and Airbnb requires it to be set to share more information for some unknown reason. This doesn't seem to be documented anywhere within the help article referenced by @Sybe .
To change this setting an administrator of the Google Workspace will have to log in to admin.google.com and go to Apps > Google Workspace > Settings for Calendar > General Settings and under General Settings change "External sharing options for secondary calendars" from the default "Only free/busy information (hide event details)" to at least "Share all information, but outsiders cannot change calendars".