Problems with enhanced features in -regex of utility "find"
It appears there is a bug in the native MacOS find in which its -regex option does not correctly handle any of the Shortcuts described in man re_format. The following command seems to work:

find -E . -regex '^(.*)([[:digit:]]{2})' -print


This slightly simpler variant also seems to work:

find -E . -regex '.*[[:digit:]]{2}' -print


In short, grep -E and finds -regex option don't seem to handle regular expressions in exactly the same way.