There have been several references to a mortal that might be stronger than a God of Destruction, both in the anime and manga. Is this person supposed to be Jiren and if so, is he indeed stronger than a God of Destruction, or is it still unknown exactly how strong he is?
The answer to this question would be a yes and a no.
So I think the best way to represent Jiren's power is to state that it is at the level of a god of destruction. Just like we see Champa hold his own against Beerus despite Beerus being stronger, Jiren would easily be able to hold his own even against the stronger God of destruction across the multiverse.
As seen in ep. 109 and 110, his power just terrified even Beerus the God of Destruction and Goku after that Ultra Instinct form was not able to defeat him. Just going toe-to-toe and dodging, but he hardly took hit which was nothing for Jiren.
I would say Jiren will take this fight as he is insanely, monstrously strong. He didn't even increase his power to the final limits.
Think about it. Jiren's true Power (on YouTube).