Looks like snakeskin/tortoise shell nail art...
The basic idea:
Prepare nails, apply base coat, cure
Apply 2 coats of a light gel polish, curing each layer
Apply 1 thin coat of a dark gel polish - it needs to look quite sheer so you can see the colour underneath. Don't cure yet.
Decant a little of a super-sheer gel polish onto a tile/foil. With a large dotting tool, apply dots of third polish to uncured layer. The dots will disperse into the uncured gel polish, creating a snakeskin effect pattern. Cure.
Finish the nail with top coat as usual.
Here's a youtube clip from Sarah R that shows the process.
For some of the nails you've shown, I think they applied 2 different colours with the dotting tool, and some of the swirls created using a smaller dotting tool before curing. Hope this helps
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