Texture2D has an undocumented constructor with an integer mipmap count, instead of just a bool for the whole mipchain, that is:
new Texture2D(int width, int height, TextureFormat format, int numMips, bool isLinear)
This way it is possible to create textures with a limited number of mipmaps, and it can be useful for large atlases to prevent leaking.
According to UnityCsReference, the constructor first appeared in 2019.2 and is not available in 2019.1, 2018.4 or any of the earlier versions.