After some more code digging and experiments I can answer my own question. A theme is a normal plugin and as such does not inherit any behavior from other plugins.
So you need to copy everything you need from the base theme library.js to your child theme. And of course, you need to declare client scripts explicitly.
Loading of missing templates from base theme is the only link between the base and the child theme.

Thanks for providing much needed assistance @frissdiegurke 😄

Welcome to the land of plugin creation @Doppy !!

I decided to go with applying the compile-step to all client-side scripts options.

Nonetheless this might be nice to have 😉

Post your plugin.json maybe it has a syntax error. Also did you put your theme in node_modules and activate it from the ACP?

gh#3534 😄

I'll have to do some more testing. Thank you for your help. 🙂

@Jelena You're welcome, didn't look in the plugin file. 🙂 glad you've got it working,