Most have a manual mechanism to operate them from the inside. Mine are a bit fancy - theyhave a motor and a remote control.

Maybe this is a weird European thing, but my metal blinds are outside, so yes, they are very effective at reflecting radiated heat away. The triple glazing does a decent job blocking convected heat and last but not least good quality curtains to block any conducted heat that makes it through. It’s never going to be 100%, but I’m confident it’s 100% better than yoghurt!

Maybe my understanding of blinds is wrong, but the ones on my window get pretty close to completely dark. Add a decent curtain (with insulation and blackout) on the inside, and I can keep the flat comfortable passively.

Whatever else you do, close the damn windows and doors during the day, and fling them wide open as soon as its cooler.