When selecting the custom type for web application backup, I'd rather have an Exclude file/folder option rather than Include.
For example, I want to backup everything in webroot except for composer and npm directories.
In addition, having an Include option can be problematic. As new files/folders are added, you need to add them to the backup as well. If you forget, it could be an issue.
By default, I'd rather see every included and then manually exclude what files/folders I don't want to be added to the backup.