I added the GUA tool as one of the installed tools. But I didn't do anything on the rule level yet. I thought we only have a empty container for GUA. All the rules won't send data to GA account. But actually we saw data from DTM. I am wandering in this case, what kind of data DTM is sending to GA? Any good document / video on how to setup GUA in DTM?
When you add UA on a Tool level, by default DTM outputs the UA library and page view tracking on every page load, even when no Page Load Rules (PLR) are in place.
If you do not want UA to load on certain pages, you can create a PLR with condition(s) to identify the pages (e.g. a URL path) and then within Google Universal Analytics tool section of the PLR, there is a checkbox labeled "Don't load Google Universal Analytics on these pages" that you can check.
So in other words, by default everything is whitelisted and you can create PLR(s) to blacklist pages.