As I said I have now visited two sites using UBB7.7.5 and the line item does not exist in the config.inc.php file.
Nor does the item exist as a item to edit in the cp.
But this site has
'DATABASE_BIG_LIMITS' => '', in the config file and when I run Prune Orphaned Private Messages i get Invalid mode specified
I am on php7.4 .
The only way for me to add a value to Prune Orphaned Private Messages is by editing the config.inc.php file
