Speed of typing, time between clicking on the search bar and beginning to type, and how fast you correct typos since that requires you to be looking at the text while typing. Maybe also some theory-free inference if they’re handing your browsing activity to ai, which they probably are. I’m not sure what else, but a lot of storefront time is typing, so they’d be able to build a lot of confidence about what your typing method is. It’s one of the few things they could learn by directly observing your actions rather than browsing history.