Android, how to backup a folder on the SD card

[cartoony]

This page says that I can simply click on + and add a folder to the backup

https://www.bt.com/help/broadband/bt-cloud/getting-set-up/use-bt-cloud-to-back-up-content-and-device...

However there is no + symbol and going in to settings I can only backup pre-specified folders, I do not get the option to add my own folder too the backup

How do I backup a folder on the SD card please?

[liamh]

I'm also struggling with this, it looks like it will only back up photos in the default location, with no option to add other folders or SD cards.