In Firefox and Chromium, when DevTools is open, pressing Ctrl+Shift+C calls the “Select an element on the page to inspect it” function. In MiniBrowser 2.34.4, when the Web Inspector is open, pointing with the mouse over the button, providing the same function, shows “Start Element Selection (^ ⇧ C)”. I guess this means also “Ctrl+Shift+C”. Pressing Ctrl+Shift+C however does nothing. See also https://gitlab.gnome.org/GNOME/epiphany/-/issues/1697.
It works for me. It's a keybinding of the inspector, so the inspector window/web view should be focused when doing Ctrl+Shift+C
In Firefox and Chromium there is no need to focus the Web Inspector/Dev Tool, before pressing Ctrl+Shift+C to activate the selection.