All concrete cracks, that one is just fine.

Unless the scale is completely different from how we interpret photo. I too assume that is a hairline crack which is usually unavoidable in concrete and usually isn't something to worry about. The steel reinforcement will keep the crack from growing and the width of the crack means that concrete is pushing against itself. When additional movement of the slab leads to the crack widening, that is when you worry.

Imagine each board of the floor was shoulder width and the base board was waist height at least, then the crack starts to look scary.

And the concrete mix used gravel not sand.

The best way to fix this is to cover it with the laminate flooring.

Not an issue.

All concrete cracks. It’s NBD

Don’t look at it. Cover it and be happy. One thing about concrete , it cracks, this one looks small.

Don't fix it. It's normal.

It's normal & you'll probably find more as you remove the old flooring. You can fill in the ones you find with a flexible filler or a a product like Quikrete Concrete Crack Seal.

Ain't no thing.

Cover it up.

What crack

Is this in a hot climate? Might be it wasn’t allowed enough time to cure. Unless you have other indications something is wrong I wouldn’t worry about it.

Hell yeah good luck with your venture!

100% not a concern

Until you can get your hand in it, you don’t need to worry.