In previous versions of EE, there was a setting in the Channels called "Maximum number of entries". However, in EE5 I can't find this setting- is it still available?
Yep it is still there. Go to
Developer/Channels and edit a channel (or create a new one) - the Maximum number of entries value is the third setting field down on the "Channel" tab (i.e. the first one that appears when you edit a channel).
More in the EE documentation.