Spawn GameObject in a radius of coordinates

I want to make a script that makes it so that within the player's radius, new game objects will spawn in a certain coordinate if inside this radius. Basically making a script that spawns new game objects in "new locations".

My original idea was that if a coordinate that has an x and a z divisible by a number, spawn a game object at that position, and is inside the player's radius.

So for example from within a radius of the player, I want to spawn a cube only if the X and Y are divisible by 20. So at (100, 0, 40) it would spawn one but at like (100, 0, 30), it wouldn't. Since these are world coordinates, I can't get a distance between all the coordinates within the radius if I would be using Vector3.distance because I don't have any specific game object target to compare distances, just a proximity of positions.

Maybe there's a way to get all the x,y,z within a radius and put it in some list so I can keep track of it that way?

Image:
Red- Player
Blue - Spawned game objects
Yellow- A certain radius
Black Dots- coordinates in the scene (x,y,z), not gameobjects
5981462--642578--image.png

5981462--642578--image.png


If you have discreet positions for the grid (spawn points) and not pixel-resolution density, then you can get away with something like this: https://www.redblobgames.com/grids/circle-drawing/#distance-test

[quote]
If you have discreet positions for the grid (spawn points) and not pixel-resolution density, then you can get away with something like this: https://www.redblobgames.com/grids/circle-drawing/#distance-test
[/quote]

The website has an interesting take on it but what I'm trying to accomplish is actually a bit problematic with this solution. I added this to my post to clear up what my problem is [quote]
Since these are world coordinates, I can't get a distance between all the coordinates within the radius if I would be using Vector3.distance because I don't have any specific game object target to compare distances, just a proximity of positions.
[/quote]
Basically in this context, I don't have tiles/spawn points