Do you think the argument that Marinette keeping certain stuff related to the miraculous a secret from Chat when she wasn't the Guardian because it wasn't her secrets to tell was ever valid? Or do you always thought the logic was flawed even before her becoming the Guardian basically made the logic even more flawed?
"Wasn't her secret to tell" is a reason that applies to personal stuff. Stuff where the main concern is "who does the one with the secret wants to know" rather than "who needs to know this information and who can't be allowed to know".
Chat Noir needs to know that information, full stop. A lot of it is stuff that's important for him to fulfill the role that was entrusted on him.
On a purely practical level, him not knowing there's a guardian means he has no one to turn to if he's in danger. Him not being allowed to choose holders means he can't get backup if he needs. Him not knowing the potions means he's dependent on others for supplying them and may not have an important one when he needs it. Hell, by s4 he wasn't even told everything the miraculous are capable of considering he didn't know what the power of the pig was.
But more than that, he's entitled to that information. He puts his life on the line every day (and outright died a few times) to clean up Fu's mess. Fu doesn't have the right to deny that information to him.
The worst part is that we can't even say for sure that it was Fu who demanded Marinette's secrecy rather than Marinette deciding on her own that this is how it should be. We never see that conversation between them, and from the conversation we do see in Syren, Marinette seems to wholeheartedly agree with the secrecy (which is a conclusion her future actions support).
Like, when Chat Noir asks her about the secrets her response is that "it's not exactly easy for [her] either". And when she brings it up to Fu all she says is "Cat Noir is asking more and more questions. He's tired of being left in the dark." She doesn't advocate for him or even seem to think he has a right to know those things. The thing she seems upset about is Chat Noir confronting her about the secrets rather than any issue she has with keeping the secrets themselves.
And we can reasonably assume that she never advocated for him off screen either. The second she says Chat should be told shit, Fu folds and agrees despite literally nothing having changed to make it the right time to "put the noodles in the boiling water". If it was that easy to get Fu to agree, that can only mean she never tried before.
"It wasn't her secret to tell" doesn't hold up as either a good justification for Marinette's actions or even as a correct explanation for her motivation. It seems more of an excuse to dismiss Marinette's agency in the entire thing.
(Although even if it was right and Fu did ask Marinette to keep quiet, "blindly follows authority at the expense of someone else" is not nearly the innocent, blameless trait her apologists think it is. There's a reason this is the trait Milgram checked in his experiments.)
Honestly, Marinette's attitude towards the secrets seems to be along the lines of "she's entitled to know everything but anything Chat learns is a favour to him". You see it a lot in s4 and onwards, but it exists even as far back as s2.
I probably don't need to tell you how bullshit that mindset is. There's not a single secret in regards to the miraculous that Marinette is entitled to and Adrien isn't. They've both been heroes just as long. They're both giving from themselves for the city. The things Marinette did to "earn" the right to the secrets were all either luck, the work of other people or her making mistakes and failing upwards.
Some stuff I can see an argument for on the grounds of "the best way to keep a secret is to tell as few people as possible about it". However, that reasoning has to be weighted against the practical concerns I mentioned earlier.
But another major aspect of the secret keeping is that by not telling Chat anything, or even advocating for his right to know, Marinette is very much throwing her partner under the bus.
Their entire partnership is supposed to be built on trust. There are many times where Chat blindly trusts Ladybug. Yet her actions communicate that she 1) doesn't trust him 2) doesn't keep his best interest in mind.
You can argue until the end of time whether that's what she actually thinks or not, but it's what her actions communicate. Trust is a two way street. You can't demand someone trust you without also extending trust in return.
Chat would have every right to see that behaviour and stop trusting Ladybug, considering she isn't even telling him anything about why she's keeping secrets. If he wasn't an abused kid already used to being treated like shit, that could've very much lead to the breaking of their partnership as a direct result of Marinette's actions.
The only thing I may be willing to allow "it wasn't her secret to tell" for is Fu's trauma about destroying the order. But even that is very iffy considering it's very important information to know in regards to whether he can be trusted.
They guy presents himself as this wise mentor trained in an ancient tradition of the miraculous. That's where he derives most of his authority from. But the truth is that he's a half trained disciple who failed the tests he was given. If his actions didn't lead to catastrophic results, he would've undoubtedly not been given the responsibility until he (at the very least) matured and was able to pass the test.
Fu's opinion is only one step above Adrien or Marinette's in how much it should be considered. It certainly shouldn't be treated as any kind of authority.
