Question

Studio One Prime refuses to open the song programmed in Studio One Artist.

Can I somehow save a song in Studio One Artist so it is downward-compatible and can be edited in the Studio One Prime. If it uses some things which are not part of Prime but only of Artist, that would be ok.

Answer 1

Songs made in Artist and Pro can be opened by Prime it just won't output audio on tracks that use features/instruments Prime doesn't have.
The only restriction IIRC are track folders.
Easiest way is to render down / freeze those particular tracks and share the project that way.
Alternatively, just activate Artist on a laptop and take it around with you (if that applies to you).

Prime also has 3 add-ons that, together, cost about 1/2 the price of Artist and bring in: Mai Tai, Ampire and a few plugins.