Here is a sentence from a schedule planner app:
In the app, you can easily group to-dos into projects and drag tasks within and between them.
I am not sure if the word "group into" is used in the sense of "add" here.
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"Group" is both a noun and a verb. As a noun, it is a collection of something. As a verb, it means the action of putting things into groups. So, we can "put things into groups" (so the collection is called "a group"), or we can "group things into..." and name the collection something else entirely.
In your example, the verb "group" is being used. The individual items are "to-dos", and the name of the groups is "projects".
It is not exactly synonymous with "adding", however, if a group already exists then yes you can "add" something to it. In your example though, it seems to be talking about creating new groups of things, so "grouping" is the right verb.