I bet you are wondering why ArcGIS Pro 2.7 has a Toolbox folder!!! And they don't contain *.tbx files (for the mostpart).
C:\YourInstallFolder\Resources\ArcToolBox\toolboxes
And inside that folder are folders with "stuff" in them for every tool in ArcToolbox.
I bet you were wondering how they go from a "folder" to a *.tbx ! Right?!
How about a blog post from the dev people on making the transition?
How about a help topic on it.