Windows Backup, one-stop backup solution doesn't work.

The Windows Backup "app" doesn't work, whenever I toggle folders/items to backup to "off", it doesn't recalculate the storage size needed, so "backup" is bigger than storage available, leaving me unable to start backup.

I have followed this guide:

https://support.microsoft.com/en-us/windows/back-up-your-windows-pc-87a81f8a-78fa-456e-b521-ac0560e32338