You might have run into the same issue as me. See this thread:
Interesting! Did you have success accessing the layers after downloading the ArcMap compatibility pack? Were these layers also available for your use within ArcPro? Thank you for your help thus far!
Sorry for my delayed response. Yes, I was able to get all the editable basemap layers by installing the data rather than connecting to it. There were a couple of things to note however:
1. In previous years, there was a Basemap.lyrx file included with the installation that was supposed to be optimized for Pro. This year there is only a Basemap.lyr (not.lyrx). Not sure if that will become a problem later on. So far it seems to be working ok.
2. When I first opened the Basemap.lyr file, I was getting red exclamation marks next to every layer. At first I thought it might be a licensing problem, but then it occurred to me that the data source might be wrong. I looked at the source for the data and sure enough, it was pointing to a location on an E: drive. I don't even have an E: drive on my computer. I simply repaired the data source by pointing it to the correct location and now everything seems to be working.
Hope you get it all figured out!