Conversations involving multiple participants, allowing collaboration and information sharing in Teams
Not a solution but a workaround, posted several times in this thread:
Open menu with three dots [ . . . ] at the bottom of chat panel (below editor), then close the menu by pressing Escape on keyboard.
Since this is just the answers forum I suspect almost no Teams/Microsoft engineers look in this thread (even if Google has it near the top of search results). Can't tell where this problem should be reported to get to the right people.