I had the same issue and when I contacted MathWorks they said it's a known issue in 2019b that is being investigated, here's their response:
The current workaround is to use "openvar" as described below. More information on this function can be found in the documentation at at
In order to test this workaround, please execute the following in the MATLAB Command Window:
>> f = figure; % create a figure
>> openvar f % or "openvar('f')
Note that if you simply click on "f" in the variable editor, only the property inspector is opened. However, using "openvar" directly opens the variable and you can click to access sub-elements in the variable tree.
