Minimize and maximize buttons missing only for certain programs in Pop! OS

Unfortunately, for some but not all programs (Thunderbird, Signal, Libre Office, QGIS) the minimize and maximize were suddenly missing and appear maximized (not full screen. I noticed it suddenly without having installed anything previously). All other programs appear with minimize and maximize buttons. Since, I have updated my Pop! OS (to Pop!_OS 22.04 LTS) and tried reinstalling the programs as well as changing the settings in GNOME 3, but without any success. Especially for QGIS without the buttons I cannot move the different window of the program and thus can hardly use it.