Whenever I am trying to take a screenshot with flameshot (by the command flameshot gui, I get this prompt saying “Share this screenshot with the requesting application”. Once I click share, then flameshot is turned on. Why is the prompt there? Is there a way to remove it?
Did you click on that Options… button? What’s behind it?
And did you save the screeshot to your local drive first? If yes, your system may be unaware of the corresponding mime-types. In that case you have to tell Gnome which app to use for handling .png / .jpg / … file-types.
If this is the case, it seems that Flameshot is registered as the only program to handle such files. You could reinstall eog, or install ristretto instead as image-viewer then, although the newer Gnome doesn’t like Gtk-apps that much, see here: https://help.gnome.org/admin//system-admin-guide/2.32/mimetypes-modifying.html.en