Terrace door: Swing door, lift-slide door, or parallel sliding-tilt door?

For me, the wing doors with overlap cost approximately €800 each plus VAT. A lift-and-slide door of the same size was approximately €1,700 each plus VAT. All triple-glazed. So you pay more than twice as much.

Offer 3m lift-and-slide door with triple glazing and anthracite exterior: Lift-and-slide door: €3150 net Parallel tilt-and-slide door: €1850 net My aunt had a PSKT; it was the worst crap ever. It was always so jerky.

Width: approx. 2 m

Is that the rough construction dimension of the wall opening?

After deducting the profile widths, there isn't much opening left between the elements anyway...

I am also supposed to have 2mx2m patio doors installed.

You have similar conditions as the OP, and the answers from 2015 still apply unchanged.

I would have the space for French doors, but I find it a bit annoying that something always protrudes into the room.

Then open outwards. I don’t see other options besides the classic symmetrical double-leaf door with mullion at this size.

Are there any other reasons that speak in favor of French doors?

See the answers on page 1, lift-and-slide doesn’t make sense here; fold-and-slide even less so, and PSK is rubbish: my former employer did not have it in the program (even though we otherwise fulfilled every special request imaginable that could bring warranty trouble).

The starting point are double doors. What should you pay attention to? What is a "must-have"? Which glazing, plastic/aluminum-wood? Safety glass? ...

Then just open outwards. I don’t see any other options than the classic symmetrical two-sash with mullion in this size.

Asymmetrical. 1/3 fixed, 2/3 opening.
Not everyone likes mullions, and they can also lead to the "compulsion" to take even more mullions so that it looks uniform.