That looks like normal roller stipple.
I don't know the kind of paint you are using, but most water-based "latex" paints are fairly thick and gooey. They tend to leave stipple and this is often a desired design effect.
You can try different styles of roller, such as a foam roller, but all will have some stipple.
If you do not want that, then the (fairly sparse) Google word is "Roll and Tip". It's mainly a term related to marine paint, where spraying is often avoided, and the goal is to get "spray look" from roller/brush.* It involves roller to quickly lay down a lot of paint fast, and then a light-handed "tip out" with the brush to remove roller stipple. I'd say 90% of my paint work is that.
However as you will see if you google it, it requires a well chosen brush, a knack, and learning how to reduce (thin) the paint just right so it flows out.
It helps A LOT that your target surface is horizontal, try it on the side of a boat!
I can tell you latex paints are way too thick coming out of the can; they are supplied thick for use with airless sprayers and everyone else is expected to reduce it. (it's easy to thin paint, but not really possible to thicken it).
* Because, often boats cannot be put inside paint booths, and larger boats are occupied and it is impossible to cordon off part of the ship to keep people away from the overspray. 2-part marine paints that come in "A" and "B" parts have highly toxic heavy chemicals in the resin. They polymerize with the A-part to create a non-toxic final coating safe enough for inside of food cans and potable water tanks. However that makes spraying rather dangerous, and requires a "moon suit" with pressurized air to protect the sprayer. Not something you can do on an occupied ship that is underway, and not something amateurs want to do. As such, marine paints come in "brush" formulations (a custom B-part with good flow-out).