You what, mate? Have we travelled back to the 19-20 season?
I appreciate Gundogan's scoring form last season might have been caused by a change of position that enabled a bit of a purple patch for him, but he's been here five years now and still consistently starts in big games. There must be a reason for that. Pep doesn't suffer fools and he clearly trusts Gundogan, so the idea that he's been "rubbish" is really extreme. Pep's had no issue dropping club legends (or selling them), he's had no issue leaving players out for weeks when he deems that they're not doing well enough. I can't recall Gundogan ever going through a phase where he was benched for a long stretch despite being fit and available. He was instrumental in the 18/19 run-in and once again in our title-win last season, while the rest of his City career he's been a decent, professional option to fill in whenever Silva or Fernandinho haven't been available.
I'm actually a bigger fan of Gundogan than most people and have often seen real value in him where others haven't, but even if you were being really critical I think the worst you could accuse him of is not being as effective as David Silva in that #8 role and maybe being a little slow to accelerate. But we know now (given how good they've both been for ages now) that the Rodri-Gundogan double pivot was suffering from more systemic issues in 2019 and had little to do with them both as individuals. Rodri was getting used to his new position while dealing with a makeshift defence behind him (remember that we had to play Fernandinho at CB alongside Otamendi on far too many occasions), while Gundogan was in and out of the side with David Silva on his last legs. It's something Pep needed to sort out by fixing other areas of the team and that's exactly what he did.
As for Gundogan being at the heart of our Champions League exits... Christ, that's a massive stretch. He wasn't even involved in the Monaco games, so scratch those off the list. Liverpool - I don't think it's Gundogan's fault that Pep started him on the right-wing and that our defence shat itself in sight of the Kop, nor the fact that we had two perfectly legitimate goals disallowed for offside over the course of the tie. Spurs - Aguero missed a penalty in the first leg and VAR screwed us over in the second leg. Lyon - I seem to remember it was Raheem who skied it from 4 yards instead of tapping in for 2-2. And I'm pretty sure it was the random inclusion of Sterling in the final last year that disrupted the balance of the team overall, not Gundogan, who had been there all season.