is opportunity countable or non-countable?

Almost any uncountable word can be countable.

I can talk of cheese and cheeses (Cheddar and Wensleydale); of bread and breads (white and soda bread); even water and waters (pond water; sea water; drinking water). I can have a number of wines in the cellar. Opportunity is like this: many opportunities can arise to do something, in which case you have a lot of opportunity. When talking of opportunities each individual occasion is considered; but together they make a lot of opportunity.

Which you use, opportunities or opportunity, depends on whether you want to focus on each individual occasion you might do something, or the concept of being able to do it.

Some really abstract concepts are not easily made countable: evidence and information come to mind.

Many countable words can be uncountable: you can have buildings built of brick.