I just discovered something new that I did twice today to try to return the printer back online. A lot of previously noted successes worked for me as well, but the offline message would return when trying to print.
I tried the "Get Help" app again but went deeper for more troubleshooting options and came upon the option to "Restart the Wi-fi Adapter".
I clicked on it and waited a bit until it was done. Then I went to HP Smart app to see if the printer was back online. It was and I was able to immediately print. It was successful twice today.
I hope it sticks and I hope this will help others.