I have emailed people based on a YouTube video, podcast episode, blog post, or just browsing a project on GitHub. If their email address is available I see that as permission to contact them for "wholesome" purposes. A few things that come to mind:

1. clarification on something in particular that they have already published

2. engage in genuine discussion about adjacent topics in which their opinion is specifically relevant

3. expressions of appreciation

4. corrections of information to prevent genuine harm or significant frustration for others

My success rate is probably 50-75% but I only do it a few times per year.

Cold-calling to get people try try your new app or answer a survey is rude.

My senior year of college, I emailed a Danish/Swedish professor (had lived in both countries and published in both languages) about a niche research article he had published that I was unable to find. He not only sent me the article, but mailed a couple copies of his books to me in the US. Sadly, my Scandinavian reading comprehension has plummeted since then and I am unable to read his books anymore, but they sit on my shelf and remind me of that period of my life and my wonderful Nordic Studies professors.