To be fair, this is a long standing issue between how Apple wants people to uninstall their app (by throwing them in the trash) and how modern apps really work in practice (some apps need/generate temp data in AppSupport, and sometimes it's a non trivial amount).
As a developer the best you can usually do is put some instructions somewhere (website, somewhere in a menu in UI), or do a package install that puts an uninstaller somewhere (more of the Windows way, but it breaks many expectations from users like having your app be one icon in `Applications`, and not it's own folder with your app and maybe a "Uninstall" app there too). For Aerial I give uninstall instructions on the website, but there's not much of a standard on how to handle this (that I know of, at least).
As far as I understand this is downloaded data and they may offer model selection later on? If so they have little choice and putting your data in the user `/Library/Application Support` (or maybe `/Library/Caches` but that's a mess in itself) is what you're supposed to do.
With the various security changes in "recent" macOS, you can't modify your bundle and download files inside it, as it would change its signature and break the notarisation system.
The latter. A model update would then just be an application update. To answer my own question - if they want to allow a choice of downloadable models, then Application Support is the perfect place.
As a developer the best you can usually do is put some instructions somewhere (website, somewhere in a menu in UI), or do a package install that puts an uninstaller somewhere (more of the Windows way, but it breaks many expectations from users like having your app be one icon in `Applications`, and not it's own folder with your app and maybe a "Uninstall" app there too). For Aerial I give uninstall instructions on the website, but there's not much of a standard on how to handle this (that I know of, at least).