Why aren't some apt packages not showing in the snap store?

The apt version of gimp is not showing up in the snap-store?

Can you elaborate on what you are asking? I’m seeing version 2.10.18 of gimp in the stable channel in the Snap Store:

$ snap info gimp | grep stable
  latest/stable:    2.10.18 2020-05-19 (273) 184MB -

i think what is being talked about is the snap-store snap …