An App Folder is a saved set of apps, and it can hold app categories and websites too. You pick one when you start a Quick Block or set up a Focus Session, so you don't have to choose the same apps every time.
Use a folder
Tap Apps to block (Quick Block) or Choose folders to block (Focus Session). Your folders open.
Tap a folder, check the apps, then tap Use this folder.
Each block uses one folder.
Make or change a folder
To make one, tap Create new folder (or Custom folder the first time), name it and add your apps.
To change the apps in a folder, open it and add or remove apps.
For folders you made, the ⋯ menu has Edit folder (to change the name and look) and Delete folder.
You can also manage your folders from Profile.
The four built-in folders
Night block, Socials, Work mode and Morning block start empty, ready for your apps. You can change their apps, but you can't rename or delete them.
Good to know
A block copies the folder's apps when you create it. Editing the folder later doesn't change blocks you've already made.
App Limits don't use folders. You pick the apps for each limit directly.
Folders are saved on this iPhone only. They don't move to a new phone.