Right Click Run this program in Sandbox option?

Is there any way we can manually run suspected files through the sandbox? Like Right Click > Run file in sandbox?

What version of avast are you using? (i.e. not the free version, no (proper) sandbox

Do I understand this clearly, that in the free version this option is unavailable?

Yes. The free version has a limited sandbox feature. The decision is based on various things (i.e. heuristics etc…) It is not as selective as the sandbox in the paid versions.

Some more info: