I got virtual desktop now. So i got similar issues there. I just changed from widescreen (1366x768) to 4:3 (1024x768) and it worked. I think, same will be with oculus air link. I will try this later and will comment, if it not worked.

Thanks a bunch, this helped. Although not at first, I had to unsubscribe from the beta program, then it worked!

I assume you have an external PCI box with a desktop card in it?

Yup. Such cards called eGPU. But issue not in card, I think. Bigscreen app shows desktop fine.

If so: maybe see and try to get your hands on a little more potent GPU, like a 1060 or 1080. Doesn't even need to be top of the line.

Sadly, no. Only to buy. But I prefer to buy something much more efficient. And certainly not for laptop. 

Since you have an external GPU, I assume you have an external PCI box with a desktop card in it?
If so: maybe see and try to get your hands on a little more potent GPU, like a 1060 or 1080. Doesn't even need to be top of the line.
Or maybe see if you can test with one to see if it even makes a difference.

Virtual Desktop: well, you can try it and if it doesn't work, you can always ask for a refund. Make sure you get this version though.
Warning: The version from Steam is not the one you're looking for!!

I'm planning to buy virtual desktop, later, one day... Hope, there will be no such issues.

I'm inclined to think the GPU cannot keep up, or doesn't support the "streaming" option (the desktop is recorded as a video, and then compressed and streamed as video to your HMD/Quest). The fact that it is an external GPU may be the cause as well, but to be honest I have no experience with external GPU's.

Did you try Virtual Desktop (native Quest 2 - link)?

its dell e6430, 16 gb ram, external gpu msi gtx970... guess it can be external gpu cause this? but im not experienced any issues with remote desktops i worked before...

Are you using a laptop? What kind of model/type/configuration?