Assigning a motive and then attacking the motive

Been thinking about what fallacy this may be lately and I can't quite place it, it seems close to Ad Hominem (Circumstantial); but also somewhat like a Strawman.

Person 1: I believe X.
Person 2: You only believe X because of motive Y; Y is bad so X is incorrect.

Example:
Person 1: I believe that abortion should be illegal.
Person 2: You want abortion to be illegal so that you can control women's bodies and relegate them to a societal role of breeder; we can't have that - therefore abortion must be legal.

Importantly note that here Person 2 is claiming that Person 1 wants to (directly or indirectly) control women's bodies; not that women will lose control over their own bodies as a result (if they claimed the latter I don't think that is necessarily a fallacy).

The reason it doesn't seem to quite fit Ad Hominem (Circumstantial) is that Person 1 does not necessarily benefit from their claim being true; except possibly in the view of Person 2 via the motive they assign. The assignment of a motive part is what makes it feel a little like a Strawman to me, but very unsure on this.

It is a combination of fallacies. It starts with a simple strawman by suggesting a motive that might not apply and attacking that:

You only believe X because of motive Y;

Then, it looks like an appeal to the consequences :

Y is bad so X is incorrect.

That is, concluding that an idea or proposition is true or false because the consequences of it being true or false are desirable or undesirable.

Right, so I don't think that the claim that the opponent has a motive or bias has to be true for the argument to be an ad hominem circumstantial<>. The ad hom circumstantial is defined as:

Suggesting that the person who is making the argument is biased or predisposed to take a particular stance, and therefore, the argument is necessarily invalid

So I think given this definition, merely suggesting a bias from the opponent to dismiss their argument qualifies as an ad hom circumstantial, regardless of whether or not there is an actual bias on the side of the opponent.
As for the strawman fallacy<>, I think this can also qualify as a strawman, as it is defined as:

Substituting a person’s actual position or argument with a distorted, exaggerated, or misrepresented version of the position of the argument.

Person 2 in your example does that by putting words in person 1's mouth in assuming that the reason why they think abortion should be illegal is because they want to rob women of choice and force them into a role of a mere breeder (which is not necessarily the position of person 1 and more likely a distortion assumed by person 2).

I can see the case for Strawman but Person 2 goes further and actually attacks Person 1's motive and secret desire to turn women into "breeders" - concluding abortion should be legal because of his suspected motive and sexist views.

So, I'm seeing an overt Bulverism here:

Bulverism

Description: It is the assumption and assertion that an argument is flawed or false because of the arguer's suspected motives, social identity, or other characteristic associated with the arguer's identity.

Logical Form:

Person 1 makes argument X.

Person 2 assumes person 1 must be wrong because of their suspected motives, social identity, or other characteristic associated with their identity.

Therefore, argument X is flawed or not true.

Person 2 should reconstruct their argument to remove the focus on their interlocutor's personal motives of biases:

Person 1: I believe that abortion should be illegal.
Person 2: If abortion were to be made illegal then the autonomy that women have over their bodies would be eroded. That outcome is undesirable, therefore abortion should not be made illegal.

Person 2 should consider strengthening the consequent by expanding on "autonomy of one's body" and also by showing that the undesirability of losing that is worse than the undesirability of abortion. Someone arguing for the moral acceptance of abortion does not need to show that abortion is free from moral disadvantages, but they do need to demonstrate that those disadvantages are less dispreferred to the disadvantages that result from denying women their entitlement to control over their own fertility that abortion provides for.