Possible to share a post by save a picture with a QR code?

[Falco]

@thoka

Could this also be implemented by choosing a qr-code provider / API ?

Yes, that would also work.

@thoka

I would appreciate pointers how to add this to a theme.

This is somewhat complex if you aren’t familiar with Discourse development workflow. If you keen on learning Developer’s guide to Discourse Themes is a good start.