I think it would be useful to have an RSS feed of network-wide activity, or at least posts, for a given network user, corresponding to the information available in the current network activity tab, e.g. https://stackexchange.com/users/305991/jason-c?tab=activity.
I propose something like
I found What other hidden or inobvious RSS feeds are available on Stack Exchange and its sites? which, while old, seems accurate (at least the feeds listed there are valid) and confirms that a network feed does not exist. There are also various related discussions linked to from there, (such as the abandoned stack2rss project), which I will not re-list here.
I looked for other feature requests for this, but all I found was RSS feed of user's posts across the network?, which didn't seem to take off, and Additional RSS feeds, which is a broader scope than this request and primarily asks for more specific, subdivided feeds.