To understand Jiren's full power, one must first understand the unbelievable gap between his Limit Break and his ordinary self.

When Jiren is introduced, he makes quick work of SSBKK, a U7 Spirit Bomb, among other things. At this point Whis already says Jiren surpasses the level of the GoD. I need to point out here that you CANNOT be about the level of a GoD if there are GoD's stronger than you. The whole statement wouldn't make sense. So Jiren is stronger than EVERY GoD, even Beerus. But this was implied already when Belmod, who was called stronger than Beerus, was stated weaker than Jiren.

We also see Jiren shrug off SSBKK Goku and SSBE Vegeta in a 2v1, literally being on the advantage the whole time. SSBE Vegeta was capable of beating GoD Toppo, who is stated to be "no different from a regular GoD". Even if you want to argue that he's the weakest of the GoDs, he is still definitely on their level. Since Vegeta beat him, that means both Goku and Vegeta are on that level. So Jiren was winning against BOTH of these at the same time. He was effectively fending off two Gods of Destruction simultaneously. Now, here's the thing. This whole time Jiren is holding back his full power. Him being above the GoD level, beating GoD-level opponents, all of this happened while his ki was suppressed.