There are a lot of ways to create seamless tiling textures. For years you did it by painting the center of the texture, offsetting the entire image by half on the x and y, and then filling in the empty space in the middle. Repeat that process until you have cleaned up any pixels that give away the boundaries of the tile.

A few applications, like Krita, eventually built pixel wrapping into a specific view mode. You would still have to paint away obvious seams, but this made it easier.

I just started using a similar feature in Affinity Photo that is very similar to the one in Krita, but with slightly more flexibility and robustness.

I know that there are countless other programs that let you do the same, but with a particular specialization in, say, pixel art, or natural brush simulation.

There is also an absolutely huge trend of actually modelling or sculpting features of a texture and then carefully setting them up to be seamless when you render out all the different maps you will need to feed the rendering engine of a modern rendering pipeline. I made a setup for Blender that makes that sort of thing much easier and faster and sidesteps the pitfalls of rendering and baking normal maps.

Then there are the procedural tools, like Substance Designer or Material Maker. They are more like programming a graphic pattern than they are like a painting program. As such, the output they make is almost always seamless by default.

There are any number of combinations of techniques that can get you to the same spot. Creating a texture that can be mapped onto some geometry and repeat forever without looking jarring or drawing too much attention to its tiled nature.

Every few months there is some new 3D graphics white paper that grabs the headlines. At least the headlines that interest the Siggraph set. Gaussian splats. A new Ray tracing method. Faster caustics. It’s never ending. You know what the real bread and butter of 3D graphics is. A simple seamless texture. Basic geometry unwrapped well. New ways to do the same old things.

I’ve made a thousand seamless textures, and I’ll make a thousand more. Maybe next time I will paint them entirely inside Blender.