Transparency of blueman - MikeTeok/LinuxMint-XFCE-RosePine GitHub Wiki
Blueman can't handle transparency by default, we need to edit the source code.
Path: /usr/lib/python3/dist-packages/blueman/main/Manager.py
Add the "Make the window transparent" code under do_activate().
# In Manager.py
def do_activate(self) -> None:
    if not self.window:
        self.window = self.builder.get_widget("manager_window", Gtk.ApplicationWindow)
        self.window.set_application(self)
        # Make the window transparent
        screen = self.window.get_screen()
        visual = screen.get_rgba_visual()
        if visual and screen.is_composited():
            self.window.set_visual(visual)
        # Existing code...