In Sahoo (2019), Ashok describes how shootout happened to police team. We can see present + flashback in single frame while he describes:
What is the first movie to show present + flashback in single frame?
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Following up on the idea of A Christmas Carol being a likely candidate I found this video from 1901 via the Wikipedia page.
Most of the footage has apparently been lost but there are scenes in the parts preserved by the British Film Institute that I think meet your criteria. It's pretty cleverly done when you consider how limited the technology was compared to what is available to film makers now.