Hi Michael. I installed 1.23 but it made no difference. It still gives the white screen when trying to create an icon. I again checked the database and there is no entry yet for favicon. If only I could get an error message to assist you!! I even tried to put the site in debug mode but find no errors in the log. I am out of ideas.
Me again. I had another Joomla system that is still on version 3.7.4, so I installed Favicon 1.23 and this time noted carefully what happens with the JSON syntax issue.
I manage to load and save the icon without a problem (and no white screens). Then the moment I click the "star"-icon to make it the default, my admin backend crashes with JSON syntax error and loops. In the database it has the same "scalar" construct. Message: Row 824 is not valid JSON. Error: (Syntax error)
So it seems as if I can create this problem every time as long as the Joomla version is 3.8.3 or earlier. So 1.23 does not solve this problem.
In the mean time I will keep on digging...Tx