Figure 1: I see that the keyhole is a hexagonal socket. After unscrewing, I took off the handle and saw that there was still a screw to be tightened (there was a hole in the fixing block, which was a through screw and screwed on the door frame), and then tightened the hexagon socket.

Figure 2. The dome should be removed to expose the screws. This screw has a plug, either the master didn't drill the plug hole deep at first, or the quality of the plug is not good. You can solve it yourself.