You need to read the plugin documentation to understand what’s the plugin do (this seems like a repetitive insistence, but it is the most basic).
Dataview doesn’t work with the full content of the files, it works with metaDATA (data + view).
So, if you want to collect some values, you need to write them in a way that they are parsed as data.
Another thing: [[todo#cat1]] is a link to a section in the file [[todo]]. Use a link in FROM means define as source the files that in-link or out-link that file. For example, if you write FROM [[todo]] you’re defining as source (the files to be queried) pages which link TO “todo” file.