For me it sounds weird, but I was wondering if and how often native English speakers use the phrase: "I find this ..." to express their opinion, like: "I find this interesting" or "I find this is a stupid idea".
"I find this" and "I find that" are both equally possible collocations in English.
However, here's the Ngram chart:
As you can see "I find it" is most common because it's a set phrase, which is used to describe opinions or feelings that you have. It's a slightly educated and formal-sounding phrase that you use to emphasize that what you're describing is your personal experience, not a suggestion that you are making to the listener. The word "hard" is especially common with "I find it".