This is EVRI's fault. I assume you are using PLS_Toolbox. They have a figbrowser function that adds this FigBrowswer menu automatically to figures. I had the same problem in R2021a. Once you open an App in App Designer with PLS_Toolbox in the path, the App is forever broken. The FigBrower code is like a virus in your App. You can try to delete the FigBrowser menu by right clicking and selecting delete. It will disappear, but when you save the App and reopen, it reappears and if you try again, you get a million error messages and App Designer freezes. Once you save the App after FigBrowser showed up, your App is largely useless as there are a whole lot of errors in the code due to FigBrowser. Easiest thing is to remove the EVRI code from your path before using App Designer. In that case you can open a clean copy of an App and work with it. If you really have to have PLS_Toolbox too, then look at the documentation for figbrowser on the EVRI wiki. They have ways to control when it shows up and you may be able to prevent it from openning in anything that is not EVRI code related.