When loading the evolution chart for acquisition report, I received the following error
 operator not supported for strings in /var/www/matomo/plugins/CoreVisualizations/Visualizations/Graph.php line 138
That seems to happen as the default value for that variable used to be a
string. Using an empty array instead fixes the issue. Not sure which circumstances lead to that error, as I'm not able to reproduce it on demo. Might also be a regression of #14332 ?
Actually I'm not sure why the default is
selectable_rows, as I couldn't find any usage of that string anywhere else.