Why my Photoshop brush pixelated instead of smooth

I had this problem and found that I had accidentally changed mode from "normal" to "dissolve". When your brush tool is active, check that the mode box on the top menu shows "normal". This solved it for me.

For me I just went to reset all tools and it fixed the problem.

The brushes you are using also may be or a low resolution. E.G. They were created in a small size, and making the size bigger than they were created to do will change the clarity. Just like low res files do when they are added onto a high res file.

Be sure you select Brush and not a pencil with "brush" settings.

Image > Mode > choose higher B/Channel

There can be different reasons for why this might be happening but you may have changed either your brush Mode to "Dissolve" or your Layer Blending Mode is set to "Dissolve".

You may have accidentally selected a different brush. This can be changed under the brush presets panel. Hope this helps.