Where would you recommend getting started with Smalltalk on Linux today?

Squeak or Pharo if you want the full image-based experience. Some distros come with Squeak but the packaging can be confused and the versions are often old. A slow and slightly janky but surprisingly useable Squeak experience can be had in a web browser at https://squeak.js.org/run/ . Older Squeak versions tend to run faster in SqueakJS.

There are tutorials all over the place however as Smalltalk is a system that, like Lisp, has dialects, they tend to be system specific. Lots of material at http://stephane.ducasse.free.fr/FreeBooks.html .

jdougan already mentioned Pharo. There's a MOOC here : https://mooc.pharo.org/