Question about DJI Mini 4 Pro Fly More Combo

It depends on the terrain how far away you can fly. However, the requirement in Switzerland is that you may only fly the drone within visual range.

The battery lasts max. 34 min. and the thing flies max. 57 km/h. This means that you can fly a maximum distance of 32.3 km in the available battery time (which is certainly less than 34 minutes at full speed - no matter...). You can never fly further away than 16.15km anyway, then you have to turn round, otherwise you won't get back at all... So it's all theory... In practice, you normally don't fly further than 1km and if you're lucky, you'll even see the drone ;-)

It depends on the firmware and whether you want to stick to the rules. Theoretically, 20 kilometres is possible. But A: you won't see them for about 19 kilometres because they're too small and B: that's theory, I think it works on a salt lake but not here in the mountains. It's exactly the same with the radios.
Landing is more problematic, the things are damn sensitive, a meadow is quickly considered not flat enough. So make sure you take a piece of cardboard with you as a landing pad.