On desktop, hovering over a username of a post or comment author shows links to talk, contribs, and block (for admins).
When I tap a username on a mobile device, these links appear briefly, but are useless, because the tapped user's user page is already loading.
There probably should be a way to get to the user talk page from a Flow comment (see also T93432), but this hover way definitely doesn't work on mobile.