Looks like 1Password 8 only allows you to export whole organsations with all the vaults you have access to. Exporting to .1pux format means you can use this script to separate vaults into their own exports.
./separate.sh 1password_export.1pux
❯ ./separate.sh 1password_export.1pux
i| processing 1password_export.1pux
i| unpacking archive to tmp
i| preparing exports directory: exports
i| processing vault Private
i| created Private.1pux
i| processing vault Another Vault
i| created another_vault.1pux
[ ... snip ... ]
i| cleaning up by removing tmp..
❯ ls
1password_export.1pux Another_Vault.1pux Private.1pux separate.sh