Configuring incremental backups with periodic full backup What cloud are you using for your backup target?
Every incremental will contain all the new files / changes. Run the full backup once a month if that works for you. As long as you're on a supported cloud for synthetic full backups, we;ll run a synthetic full and create a new backup set and then the incremental backups will continue for another month. But if you're not using a cloud with synthetic backup support, we'll need to run a new full, which is not something you'll probably want to happen - hence my question at the top of this post.
You keep backups using two options in the new backup format: Use the Keep Backups For option to determine how long you keep backups on disk (say 90 days) and use the GFS options to determine how many weekly, monthly, and / or annual backups you want to keep for short-term and longer-term retention.
As I mentioned, the legacy backup format for files is version based and is incremental forever, but you lose many of the newer features. But for some customers, that format is preferred based on their needs. You may want to go through the backup wizard using the legacy format and review the options to see which is best for your particular need. It may be based on your description above.