Found a way. It is the “window browser select notes” feature in the Customize Keyboard Shortcut add-on.
It actually searches for the note currently selected in the Browser, so in Cards mode, it shows all the cards for that note and nothing else. From memory, that is the way it worked in an ancient version of Anki way except of course there was only Cards mode back then.
By the way, this can sort of be considered Part 2 of the topic below.
So I can hit B and then immediately use my “window browser select notes” hotkey so it shows only the cards I am working on so I can, for example, preview all the cards from the main Browser window, after changing the note type.