The rules text is ambiguous and cannot be objectively decided
This question comes down to what it means to “replace one spell,” as described in the second paragraph of each of Psionic Spells (Tasha’s Cauldron of Everything pg. 67) and Clockwork Magic (ibid. pg. 68), but the English text used here is fundamentally ambiguous on that point. There are two possible understandings of the text:
You “replace one spell” you know, having learned it from this feature, but only as far as which spell you know and which spell you don’t. The former spell is no longer known by you, but remains one of “these spells” that “counts as a sorcerer spell for you, but [...] doesn’t count against the number of sorcerer spells you know.” After all, it was one of the “additional spells” “You learn[ed]” “as shown on the Psionic [Clockwork] Spells table.” It therefore remains a sorcerer spell for you (and doesn’t count against your sorcerer spells known, but then of course it wouldn’t since you don’t know it). In this case, since it is a sorcerer spell for you, it is only your sorcerer spell list.
You “replace one spell” from the set of “these spells,” and it changes for all the purposes mentioned in the previous paragraph: you learning it, it being shown on the Psionic [Clockwork] Spells table, it being a sorcerer spell for you, and it not counting against your sorcerer spells known. Since those terms no longer apply to the spell, nothing about this feature makes it a sorcerer spell or adds it to your sorcerer spell list, and so it isn’t (unless it would be for some other reason).
In favor of interpretation 1, one of the properties of “these spells” is that they are “shown on the Psionic [Clockwork] Spells table,” which you obviously aren’t actually editing—the spells shown in the ink printed in your book are going to remain the same no matter what you do. Also in interpretation 1’s favor is the simple fact that interpretation 2 is putting a lot of weight on the word “replace” when it isn’t at all spelled out that we are meant to—interpretation 1 requires us to read a lot into that word that isn’t actually present in the text.
In favor of interpretation 2, not applying the “counts as a sorcerer spell for you, but [...] doesn’t count against the number of sorcerer spells you know” rule to the new replacement spell raises a number of questions—can you cast it at all, if it isn’t a sorcerer spell? If so, does it count against your sorcerer spells known? Clearly, interpretation 1 also implies that the rules text is missing something important.
The best ruling is that the table is added to your spell list
There are a few reasons DMs should rule that these sorcerers can use spell scrolls of these spells:
Most fundamentally, because of what “a spell on your spell list” represents—that is, a spell you could have learned, but haven’t necessarily done so. There is no question that a sorcerer who has chosen to not learn lightning bolt—or hasn’t even yet gotten the chance to learn it, though that introduces unreliability into the maneuver—can nonetheless use a spell scroll of lightning bolt. Thus, by the “spirit of the rules” for spell scrolls, the spells on the Psionic Spells and Clockwork Spells tables should be considered “on your spell list” when you have the appropriate subclass.
Also, there is historical precedent here: the “v.3.5 revised edition” of D&D had similar rules for scrolls (and wands and staffs and other such items; there were quite a few), and the rules for options like Aberrant Mind or Clockwork Soul were more explicit about this kind of thing, often saying explicitly that additional spells were added to your spell list. D&D 5e is—in general, not just this case—less explicit, as part of their overall work to limit the complexity of rules text, but there is plenty of precedent for specialized sorcerers to gain the ability to use magic items of new spells even if they don’t choose to learn those spells themselves.
Note this necessarily means mentally noting that each new replacement spell also “counts as a sorcerer spell for you, but [...] doesn’t count against the number of sorcerer spells you know,” which is not stated in the text. That makes this ruling more than just an interpretation—ruling strictly on the text interpreted per interpretation 1 would cause those spells to lack these properties and thus raise many questions about how they should be handled. Really, these are the only plausible answers to those questions, but it’s worth pointing out that these answers aren’t clearly in the text.