Why don't you show it, just log of a

[yuhaoxuan_yu]

Why does the texture not show, only loga M or A (MAYA 2020 Mtoa 4.1.1.1)

[Stephen.Blair]

Because swatch rendering is disabled be default.
You can turn it back on if you want, but you may find that it slows things down.

[Stephen.Blair]

Also, there's a known issue with Arnold swatch rendering in Maya 2020. It doesn't work.