This problem does not happen in blender 2.83 but comes up in 2.90. So I would append the brushes as shown with the fake users Checked.
After that, I would be able to see it in the sculpt tab as shown and I will save it as startup.
However, when I restart blender, it will shown nothing and the brush will not work as intended.
So my question is, with blender 2.9, is there a new way to import sculpt brushes? If so can some provide the solution.