How do you theme Sharepoint 2019 with Modern exp?

My question is quite simple: how do you do (or which strategy do you have) when you theme a SP2019 Modern in prod env?

Since site design doesnt work in SP2019, I wonder what the easiest thing would be for site admins to change the colors etc on their sites, and newly created.

Upload a customized theme in the classic look, and use that for the modern sites maybe?