Ok, so what actually works is:
In OAuth consent screen, I moved Publishing Status of my app from In Production to Testing
A new field "Test users" appeared. There I can put my test users
I have to put the same users in the Store Listing "Draft Testers Email Addresses" list.
Then those users will be able to see the workspace.google.com/marketplace/app link and install the plugin.
"Very intuitive"...