How to validate the idea if we have MVP?

The idea (shortly)

I love newsletters as a source of day-to-day news but I faced a total lack of control over this and recognized a field of huge optimization. The whole idea is about third-party UI for reading newsletters as a Facebook-like newsfeed. So the pet project has been started from our own pain and I didn’t mind doing any market research etc.

Where we are

Now we’ve built MVP and, no matter if there are a lot of things to polish it’s already something usable, however, the only users as we are, and from some point, I decided to try that product on the outside market.

What to do next

As far as I can imagine the process of idea/product validation I see the next steps:

We need to conduct some market research to identify TA and the relevance of the idea itself
To get feedback and the direction to move we need to expand our userbase with some early adopters who are okay with beta testing our product

By the way, since we need to bring some value as an exchange the feedback we might perform some “cross-beta” with other early-stage founders.

Questions to Indie Hackers

Since I’m zero in marketing I’m a bit frustrated about where to start, here are some naive ideas:

Do you think we need to perform market research and identify TA more specifically than “guys like us”? If yes what are the expected outcomes and the next actions?
Or maybe should I reach in cold founders and “guys seem to be interested in the topic” with the beta testing suggestion just to get at least any feedback.
I know that polishing the solution at first and adding the most valuable (as we think) features on top of it might be a good idea, but anyway I need to validate that there is some audience for the app, how do validate it?

This is our very early stage LP, I would appreciate any feedback on this as well!
https://andreibazhin.notion.site/Feedster-The-next-generation-news-reader-ae810adc8efd41bb86a4a0e2515f059c

And of course, I welcome any critics and advice!