Steps to reproduce the issue

Banner component & module 'Select By Keyword' not working if there is No Client selected. e.g. adding keyword 'all' to an article and adding the same keyword to a related banner while choosing 'No Client' in the module results in no banner showing.

Expected result

Banner is shown when 'No Client' is selected and Select By Keyword is selected

Actual result

Banner is not shown

Additional comments

As per conversation in #40987 and initially raised in #39016
Error with no client selected is
Warning: Undefined array key 4 in ----/public_html/components/com_banners/src/Model/BannersModel.php on line 231
Also showing a 1064 error on the homepage only of my particular site, screengrab attached (other pages no error unless debug is on and max error reporting, banner just doesn't show.