Apart from your incorrect spelling..... :)

"Opportunity" is one of those tricky nouns that can both countable as well as uncountable. Therefore the grammar is "correct" in both examples.

If you search for and go to "Google Books Ngram Viewer", and put in those two phrases, you will find that, for a time in the middle of the 20th century, use of "plenty of opportunity" reached over double that of "plenty of opportunities". Recently however, they are close to each other, with "plenty of opportunities" just slightly ahead.

The "Google Books Ngram Viewer" is a very handy linguistic tool!