Problems with BlueDiamond 1.08 and WordPress 5.8.1

I have updated Wordpress to version 5.8.1 and the BlueDiamond 1.08 theme has problems with:

Declaration of DropDown_Nav_Menu::start_lvl(&$output, $depth) must be compatible with Walker_Nav_Menu::start_lvl(&$output, $depth = 0, $args = null)

Does anyone know something about this?


Have you contacted the theme author for the free support?