Using find in macOS terminal with regex

There are a couple of issues here. Firstly, as John mentioned, -name does sub-string matching with globs, you need to use -regex, and secondly, there are regular expression dialect incompatibilities. By default GNU find uses Emacs regular expressions and BSD find uses posix-basic regular expressions. If you have find.info installed you can read more about it here:

info find.info 'Reference' 'Regular Expressions' 'emacs regular expression'

Supported regular expression dialects can be found here:

info find.info 'Reference' 'Regular Expressions'

Here:

* findutils-default regular expression syntax::
* emacs regular expression syntax::
* gnu-awk regular expression syntax::
* grep regular expression syntax::
* posix-awk regular expression syntax::
* awk regular expression syntax::
* posix-basic regular expression syntax::
* posix-egrep regular expression syntax::
* egrep regular expression syntax::
* posix-extended regular expression syntax::

GNU find

You can make your expression work with posix-extended like this with GNU find:

find . -regextype posix-extended -regex '.*[0-9]{2,4}x[0-9]{2,4}.jpg'

Output:

./1_2-600x600.jpg
./1_2-802x600.jpg
./1_2-600x449.jpg
./1_2-300x224.jpg
./1_2-768x575.jpg

BSD find

I don't have access to BSD find, but I think this should work:

find -E . -regex '.*[0-9]{2,4}x[0-9]{2,4}\.jpg'