MVP is done. What to do next?
Let's say, you have an MVP. In a perfect world, you've built it in a month. Now what? Spend 2 more months
to build fancy stuff and make it as 'done' as you'd like
it to be? Maybe put it on hold until raising the capital?
Nah man, it won't work well.

The 'MVP done' stage is not about jamming features that you skipped at the very beginning. Neither a thing that you build only once and the job is done. It's more about constantly testing the market and learning from that.
With something very small and simple that you can build in a damn month
1. Get out there
House, office, whatever. Then talk to real people. Reach out to ones, who, you think, may pay for the product as it would solve their problem.
Having 10 people who can buy the app is a good start. I mean someone else but your mom or best friend
Once you reach out to potential customers, let them test your idea. It might be a demo you give someone over lunch or trial version. I mean giving something tangible right into their hands.
2. Gain feedback along the way
Get to know people's feelings and wishes through questioning. Use the superpower of open-ended questions to get more detailed feedback. Ask something that requires more than 'yes/no' response.
You don't need to get tons of compliments about how good your app idea is. Getting 'good results' never means having
a good conversation. Everything you need is to get to the truth. Even if it hurts.

By saying 'get to the truth', I mean something like:
Them: 'Kinda cool. Love it.' (compliment that costs nothing)

You: 'Oh btw, how you handle this issue now?'

Them: 'You know, we don't have such an issue. We simply don't care.'
The worst thing that could happen is zero people to talk to. Although, even with bad or no answers, you're still on to something. Because a day of real conversation (at least, a try
to talk to) is always better than weeks of philosophizing.

So once again, ask anything that matters. Because you're not them. Because they'll give you a clue on what to retain or let go. Not vice versa.
Just stop philosophizing and get to the truth
3.Measure results and learn from that
Capture feedback to make future iterations better.
Functionality is ok, but design is a disaster? → Refine it and give the app an aesthetic appeal.

10 users have the same issue? → More likely need a fix.

Just one user encounters a bug? → Ensure it's not specific
to that user's device.
Here's the one thing to clear up. It's not about building every feature just because someone 'won't buy your app without THIS'. Refine what 80%
of users ask for. Crude, but very useful.
Dead simple 80/20 rule would save the situation here, huh?
As for the metrics to rely on, the answer is simple — it depends. It really depends on your business goals and the type of product you build - regardless of what you choose (sign-ups, reviews etc.), it should be comparative and understandable. And, yes, it's just an MVP, so high numbers would happen somewhere else.

If the idea fails (poor outcome plus zero or bad feedback), junk it. Or try pivot. Actually, there's almost always something you can do until you succeed. And of course, as long as you have money in the bank:-)
MVP is NOT the same as the Sims
This isn't a game where you can spend the whole time designing every nook and cranny
When it comes to businesses, there's no such thing as ctrl-shift-whatever cheat code that would bring you infinite money.
So, simply roll out with the most basic 'home' version and play with it. Once you expand you can dither with colors and knock down the walls. Iteratively. Room by room, here and there.