Hi i am also having the same issue with my bosses machine running latest update version 1912 build 12325.20344
if he adds more search criteria like from, body, attachments. When clicking away from the search area it does not minimize but stays the same size on my machine with same update it minimizes when i click away. The search bar with all the specialized search criteria is also appearing on his people page and refusing to minimize.
@B_Van_Spanje hi i was specifically talking about the focused inbox option, i ended up solving the search issue by doing an online repair of office. which as far as i understand is a reinstall. I hope this helps someone.