I don’t know if this is a bug with High Sierra, but when I go to export in Adobe XD, I only have the option to export as the last format I exported (e.g. only PDF, or only PNG). It took me a while to find out that if I export, and then re select the Adobe CC Files folder, that I get the choices back. At first I thought you had deleted the export to PDF function. I went to HELP, inserted PDF, and it told me to ‘Print’ to PDF – very helpful when there is still no PRINT functionality in XD.
We are aware of this issue on High Sierra. The next public release of XD will have with a fix for the export dialog.