Omphalos is a speculative (and oddly specific) scenario purposfully constructed to dismiss overwhelming evidence for an old earth. Drawing analogy to a speculative bellybutton, the argument is that God created a world with “maturity” so it would be “immediately useful” and as a “test of faith”, and then we misunderstand that maturity as old age ( Is apparent age biblical ). The “Deceitful God” objection (DGO) argues that this means placing a false story in the evidence. This is most obvious in things like distant starlight (where we see, e.g., supernovae that could never have happened), and other artifacts that appear to have no reason deriving from the “immediate use of the world”. The “test of faith” argument is suspect too, and has generally speaking been roundly dismissed (even by YECs) even though there is no replacement “purpose” offered.
Even then, from a theological point of view, there may be some reasonable rejoinders that give better purposes than “test of faith”. The 100 Year Old Tree A Lutheran’s Artistic Tree and more recently John Sanford’s Designed Ambiguity. I do not necessarily endorse these points of view except to point out that this is under considered.
Regardless, the only reason to invoke Omphalos, historically, is to dismiss overwhelming evidence contradicting one’s hypothesis.
DGO has never been meant to imply that perceptions always match reality, especially our perceptions of miracles in the moment they occur. Applied the way you are using, DGO would be valid objection to Jesus creating wine from water, because this presents a “false history” the created wine, as if it used to be a grape, etc. DGO would be valid objection to the Resurrection, because it would give the appearance Jesus was never dead. DGO would be a valid objection to anything outside the natural order, and it puts an odd requirement on God to declare all His movements that we as limited humans have access to immediately without any confusion. DGO, therefore, really needs a clear delimiting principle, or it can be applied to just about everything, including valid science and just about anything we personally find surprising.
Because their is absolutely zero evidence for or against the de novo creation of Adam, it is not valid to equate it with the Omphalos argument or invoke DGO. The problem with Omphalos is not primarily about Adam’s development (which should be considered on its own merits), but rather the use of this speculative scenario (as I read it, Genesis says nothing about bellybuttons) as a reason to reject the evidence for an old earth. As @Jon_Garvey has often pointed out, a de novo created mature Adam would be essentially no different (in terms of DGO) as the water to wine miracle.
Perhaps there are valid objections to a mature Adam being created de novo, but those objections are distinct from DGO, and have to be considered on their own independent of the overwhelming evidence for an old earth.