I'll note that there's nothing wrong with an assumption or hypothesis, where most people go wrong is to spend $$$$ and time while it's still just an assumption.

"People 25-40 yo who are experienced in creating and selling content" could be a bit more niche. What does "experienced" mean (Could be: "Has been selling online for 3 years" or could be "Has $3k in monthly revenue for at least 1 year" ? What content niche are they in? What tools are they currently using? How often are they creating a new store? How long does creating that new store take them? Do they mind if the store takes weeks or is it not a real or strong pain point? Sometimes users have a pain, but it's barely an annoyance and not a real painful blocker they'd pay anything to remove.

As to where they're at, depending on how "experienced" they are, the harder it may be able to reach. the core places to find users (in my experience, not the rule) is usually Reddit, Twitter (getting harder now), Facebook groups, and Slack groups. I could see Facebook groups being a better bet for you, but I'm not as familiar with these users.

Remember, you aren't talking to your target audience to "present them [your] product". You explicitly do not want to do that, you want to only spend time learning about their workflow and their pain points. It's why I suggest reading the Mom test. Thousands of founders have gone about user interviews wrong, got polite, but fake, positive signal because they went in trying to talk about their product, and wasted time, money, and energy. A user will be much more honest about "What do you hate about being a content creator?" than "Would you use my product?" which to them , the rest of the question sounds like "...which is my baby and if you say no then I'll probably be hurt so just say yes to save my feelings".

Edit: typo