This is Benjamin Moore, Aura Bath and Spa, bought this about two weeks ago.

Used half a gallon last week for a first coat of paint in the bathroom.  It’s been sealed since then in an air conditioned space.

Does this look good?  Can’t tell if it’s mold, paint separation, or something else.

https://imgur.com/a/MF0ZJFI

stir it up and find out. Looks like its just separating and needs to be mixed back up

This, some tints just dont stay in suspension very well.  One of my jobs we're using a very dark
purple on some trim (think eggplant color) and every time I open the can, it's got bright pink
floating on top

How would I know if it’s good after re-mixing?

If it looks like it did when you used it the first time.

(Not sarcasm).

Paint a small section and examine.

Thinking back, I bought the paint maybe a week before I used it.  When I opened it up there wasn’t any paint separation like this.  Now, a week after I used it (two weeks after purchase) it looks like this:

Does that seem normal?

In DIY unexpert opinion after 35+ years of household painting. No, paint is fine at that age. Shake he hell out of it and test a spot. Let it dry before you judge. In general, paint darkens as it cures/dries.

ETA: just saw first photo. What does it look like after remixing?

I’m going to wait and see what the paint counter says in the AM.  I’ve not seen paint separation this bad within two weeks.

I just finished up some interior painting and it has been an exhaustive endeavor. First off I used the paint the previous owners left behind and it looked bad and smelled bad, but I mixed it up and used it and it didn't match at first. I thought, I'd let it dry and it'd match up.....nope.
I went to several paint stores to try to get the matching colors and could never get it right. I would use it on several walls thinking it'd dry and match up, but it never would.
Finally we contacted the builder of the house and got the paint codes and what store they bought the paint from. Could still not get the color to match perfectly and was told the manufacturer went to a different supplier....(?) so it was hard to match it up.
I ended up cutting a section of painted wall to take in to get a match, finally got it right but my mistake was only buying one gallon, I should've bought a 5-gallon bucket of it. I used up the gallon and went to get more and again, no match from the same store using the same paint codes and even brought the empty can of the matching paint to the store and they had to experiment to get it close, but it still did not match up.
I'm thinking h*ly sh*t, they have ONE job, match the f*cking paint color! So out of frustration and wanting to finally finish the project after a year and a half of attempting I just gave up and painted entire walls with the different tone of paint and leaving the adjacent walls the previous tone.
Everyone I tell doesn't notice until I point it out to them, but I certainly can see it and it is annoying as hell.

The only time I've dealt with "bad" paint, it was because it had been exposed to freezing. The result was
horrendous and time-consuming, I've not bought a drop of paint from Lowe's in like 8 years because it's
their handling that ruined it.

Most paint that I use do not seem to seperate, but that one color did and works just fine. I'm not a painter
myself, just have to do a bit here and there when it's more intricate stuff.

ETA: and BTW, everyone should have one of these around:

paint mixer

Doesn’t look normal. Almost like ‘oil and water’ condition. Was the paint can white, or custom tinted? A latex paint, especially white or lighter colors, will stay color mixed for weeks if not for a couple of months. Oil based paints will separate quicker. Maybe the wrong colorant base added to the paint.

Our shop has three different tinting machines: computerized for latex paint, manual measurement for oil based and epoxy based paints. The epoxy paints will separate in two days.

For what you already painted, did it dry properly?

Yes, it seems to have dried properly.

I took it to the paint counter and they thought it looked fine after mixing but I asked them to replace the can anyway

It should have been shaken at the store. Then you stir again, thoroughly before every use. I like to shake then stir.