Not true.
I played twenty years as a keeper. Not to a great standard, but I do read the game from a goalkeeper's perspective and we Sunday League keepers are an analytical, self-critical bunch.
A goalkeeper will always be pissed off to be beaten low from outside the box. It's a great strike, but i think there are at least five keepers in the league that stop that Groß effort last night. That he didn't dive for it is, I think, damning. Flekken is conceding more strikes from distance than I think he should, strikes that called for good or excellent saves but which were not un-saveable. I am thinking of the second Spurs goal, the second Liverpool goal, last night and at least one from the US tour against Fulham. That's about the quality of his concentration, footwork and reactions.
There have been other quite avoidable or just odd goals conceded- for example against Palace, and Jarrod Bowen's the other week. Not to mention the fiasco at Newcastle and his failure to command his six yard box against Everton. There is enough evidence, at the least, to justify the debate.
I don't actually blame him for the Forest goal, which I think was a freak. His positioning could be justified there.
He's made some good saves, but not many very good ones that I can think of. I think we've seen enough of him now to firm an opinion, and imho he is far from a top end of the Premier League goalkeeper.
I accept there's something in the argument that his biggest problem is that he isn't David Raya, but the extent of the drop off in quality is really disappointing me.