Exclude database form AG Backup
As seen on ola's Site, you can exclude backups by adding , -database.

An example of this:


  USER_DATABASES, -Db1  All user databases, except Db1


Or in you case, with ag databases:


  AVAILABILITY_GROUP_DATABASES, -Db1 All availability group databases, except Db1


EXECUTE [dbo].[DatabaseBackup]
@Databases = 'AVAILABILITY_GROUP_DATABASES, -Db1'
@URL= xxx,
@Credential = xxx,
@BackupType = 'FULL',
@Verify = 'Y',
@CleanupTime = NULL,
@CheckSum = 'Y',
@LogToTable = 'Y'