De-classifying a document for regular people typically means that the original classifying authority (i.e. the people that declared it classified int he first place) have to say it's no longer classified. But the President is above all of them so normal policies doesn't apply to him. He can do as he wishes and nobody below him can constrain him with a policy that they wrote.
One thing I've noted in recent years is the propensity to overclassify things. By that I mean if you read the security classification guidance associated with a thing it will tell you what is and isn't classified but it you look at documents you will see many that clearly aren't classified (per the guidance) marked as classified anyway. I tend to think it's to keep them from being subjected to FOIA or something and it's a problem because it really hinders the ability for people to share information. But if you want to get that document properly marked as unclass you need to get the originating authority to agree to it, which is a pain in the rump and they usually won't bother anyway. Nobody wants to stick their neck out in government.
I think Patel and Baier are both somewhat correct, and are caught on the difference in “declassification” and “releasing to the public”. Trump reportedly “declassified” many documents relating to the plots against him, but agreed that they had to go through a careful review process before release to the public. The review is supposed to protect private individuals, genuine intel sources, etc., by redacting identities. Since the same DoJ that plotted against Trump handles the review process, they have simply not done it.
Since Trump held documents for 1.5 years without releasing them, it’s a tough sell to claim he was creating any sort of risk or reneging on his promises due to DoJ intransigence. But since they know what he has, I assume they fear he was going to rain grenades on them during the 2024 campaign.