I had this same issued today as I tried to install on a fresh Ubuntu Server install (20.04). The fix I found was this....
https://appuals.com/cannot-connect-to-the-docker-daemon-at-unix-var-run-docker-sock/
I use Termius for terminals, so while the original install was running, I opened a new terminal to the server and ran the following commands....
sudo systemctl unmask docker
systemctl start docker
I then went back to the install (log) window and BAM! It was installing like a champ. I might have to do the --redo command, but I'll check after it's done installing.
Hope this helps someone...Cheers!