Thanks for reaching out. I found a similar discussion which you can refer to here: https://community.adobe.com/t5/adobe-xd/how-do-i-export-at-4k/m-p/10511426?page=1#M14420
I also found an article sharing more information: https://medium.com/thinking-design/protip-exporting-assets-in-adobe-xd-c586996de703#:
Let us know if this helps or if you need any further assistance.
Create an artboard that is 1920 x 1080.
You'll get a 1x and 2x file. If you don't want the 1x file, simply discard it.
So, in this way, 2x is 4k?
Yes. 4K resolution is 3840 x 2160 pixels.
1920 x 2 = 3840
1080 x 2 = 2160
You may want to learn more about how this works on my blog post Retina Web Graphics Explained: 1x versus 2x (Low‑Res versus Hi‑Res)