Go to https://commons.m.wikimedia.org/wiki/Special:EditWatchlist ("List" tab of Watchlist via mobile view) and then see that uploaded files (see also https://commons.wikimedia.org/wiki/Help:Namespaces) are not listed there. Instead, if you add any page belonging to "0" (or main) namespace, like https://commons.wikimedia.org/wiki/Bradley_Cooper, into your personal watchlist, then you would see that page listed there (until you un-watchlist it). The "0"/"main" namespace comes from Wikipedia: https://en.wikipedia.org/wiki/Wikipedia:Namespace
Also, go to https://commons.m.wikimedia.org/wiki/Special:Watchlist and then click "Pages" tab; you'll see that only pages belonging to the "0" namespace would be listed there. To see uploads and "Commons:" pages, go to either "Other" or "All" tab. However, the pages are harder to search on the mobile watchlist, especially if a watchlist contains hundreds or thousands of uploaded files (and some other pages).
I previously addressed this at Commons's VP but hadn't received a reply. Here I am readdressing this.
I should see uploads and/or "Commons:" pages listed as "Pages" or, separately, "Files"