Can a lift-and-slide door be as airtight as a normal door?

A gutter "in front of it"?

Where exactly?
And: a gutter for what? Water?

Yes, impact/rainwater. These gutters are preferably avoided.

and also people who are not familiar with the technology can quickly get along with it.

I can’t manage the modern elements (lift-slide ones?) at all. Wherever I try to operate them, the owner comes running in shock because I might break something :p

I can’t handle the modern elements (lift-and-slide-?) at all. Everywhere I try to operate them, the owner rushes over in shock because I might break something

You probably mean parallel-sliding-tilting.

You probably mean parallel slide-tilt.

No idea :D They seem to tilt towards me when I want to slide them shut. But whatever: if the OP finds them easy to handle, that's okay .

They practically come tilted towards me

Yes, exactly, the lift-and-slide doors do that better, they don't tilt

In the meantime, I have taken a closer look at the door's mechanism (I could have done that a long time ago :rolleyes:) and am pleasantly surprised by the sensible idea: When the door lifts, it lifts off at the top from a running rail that is conical in cross-section (it can be moved), and when lowering, this gap closes again. At least air exchange is probably reliably prevented this way. (I could have thought of that a long time ago... :rolleyes:) I think it works, the system :cool: (the brush seal is not the actual seal but probably helps mainly against dust and insects)

I can't handle the modern elements (lift-and-slide-?) at all. Everywhere I try to operate them, the owner comes running in shock because I might break something :p

I hope it's due to knowledge of the door mechanism and not your fine motor skills ;)...

I think the system works :cool: (the brush seal is not the actual seal, but probably helps mainly against dust and insects)

That's right, the bottom rail is part of the sealing system, there are even models that are resistant to driving rain. The top seal is lifted and lowered, which makes it easier to handle. There are no fundamental problems left to solve, so you can find good models.