If you agree that they are, in fact, canonically game mechanics, then you agree that Undertale is canonically acknowledged as being a video game, and that the Player is thus a fairly literal contextualization of us within the verse's setting, instead of some entity that acts as a stand-in. Either you try to justify it all as in-verse mechanics that resemble the workings of a videogame, or you effectively agree to that thread's proposal. I really do not see how any middle ground exists here.
This is the greatest example of non-sequitur, or in worse terms, "false equivalency".
No, the mechanics of the game being canonical to the lore and world of Undertale does not equate in the very concept of a fictionalized video game also being a canonical fact in the view of said characters, or inside the world. No, one doesn't justify the other, you're making leaps in logic.
All the mechanics being canon do is telling us how their reality operates, that the mechanics are translated to tangible reality from the perspectives of the fictional character. This does not escalate to anything othet than what has been shown, and the game never ever talks about itself as a "game" from the viewpoint of its characters. The whole premise is based on a false connection, and a middle ground is perfectly in sight, as one does not result in the other, again.
Really, this is just what the crux of the thread is:
I will do a fun little experiment, and count how many unsupported and untrue statements you make in the following sentences.
Undertale is canonically a videogame
Unsupported.
and the Player is acknowledged as an actual entity with an effect within the setting
Mostly unsupported, we're not viewed as a player, we're viewed as a fictional force outside of the universe, not necessarily said force will be of higher existence in relation to the verse.
and therefore the profiles are to acknowledge exactly what this entails. So far I haven't seen a lick of proper reasoning supporting the claims that Undertale is not actually acknowledged as a videogame and that all of the verse mechanics are just things that happen to resemble video game elements (Something that is far more of a leap than just saying "Yes, those are just the game mechanics being canonized into the setting.")
What should we prove a negative? You seem under the very strange confirmation bias that, because something resembles a concept, then said concept must also be applied.
No, not at all. A verse which has video game elements as real mechanics that character must follow as their reality does not mean said verse is canonically a videogame from the perspective of the fictional setting. This can be viewed in various Isekai, or RPG Anime and Novels. Of course, the example isn't 1:1 with Undertale, but it's just to show that elements like these appear in other forms of media without the conclusion being that.
A verse which has computer-like mechanics that a character must follow as their reality does not mean the verse happens inside of a computer.
I could go on, and on. But the conclusion is simply false, Ultima.
That doesn't necessarily preclude the existence of a literal Player, no.
It does acts as a rebuttal to the evidence used to prove as such. The anomaly is directly mentioned as an anomaly, and is very clearly meant to be our influence, thus, all the evidence that suggests the characters are referring to the player automatically gain another explanation, that in fact, the characters are speaking to this fictional anomaly, thus making this already sketchy evidence to become even sketchier.
It doesn't negate the probability of a literal player, but that has not been proven yet, there isn't even enough evidence for a "possibly" rating on the respective profile, much less a solid one.