You can just upload it to some cloud repo such as Dropbox or Google Drive and share the link.
And yes, try to copy it directly from the SD card.
Did it work before?
Are you or were you able to upload other logs?
Did you do a software update since then?
I know that with my current setup, when I download a .ulg file from QGC, it is downloaded with a .px4log extension that I have to change manually. It's also maybe the case for you.