potential customers(decision makers) are generally tech leads, frontend leads in larger companies. They hang out in subreddits & some slack communities. React/Vue/other frontend meetups are a good point as those people usually hang out there - thanks! anyways, even if I know where they hang out - what are some not-annoying ways of approaching them?

I would say, monitor the conversations in those groups, find the pain points for them and see how your SaaS can be used to to solve them. Be honest, don't be pushy, set the real expectations.

Just be annoying.

If it's a business, I mean.

In those cases where your proposition solves an important problem, you are being helpful, not annoying.

Most of the time, even if you are not annoying the answer will be "No."

Rejection is the norm in sales.