Every other email app on iOS does this, even the native one. Why don’t you?
There should be a number in the top right of each bubble indicating how many new emails there are. You should be able to toggle whether this number indicates the focused inbox only, or all emails, and you should be able to toggle this on a per-account basis.
ADD YOUR ICLOUD EMAIL ADDRESS TO ACCESS THIS. ITS ALREADY A FEATURE.
This is already a feature. Add your iCloud account in order to access this.
Just like outlook for pc can already do.