He is probably looking at US sites, and clearly, indisputably, Trump opposes trans rights so from that perspective, he will think that any narrative that isn't pro-unlimited trans rights is pro-Trump.
To understand the situation properly, he needs to free himself from a US-centric view and sources, and understand the concept of conflict of rights. Yes, trans people in the US are opposed by the far right, but so are women. It's not an either/or.
If it was my child, I would probably start by explaining that, because if he just reads a lot about Trumpian right-wing attacks on trans rights in the US, he'll just think you're being stupid or are really ill-informed or biased.
He needs to understand he's not wrong on that, but that women's rights are also under attack, and that some right-wing MRAs are using trans rights as a vehicle to attack women's rights. I'd also show him lots of examples of trans people who themselves are strongly on our side in the debate. So he can see it's not just you being a bigot, but that many trans people themselves do not find the onslaught on women's rights and the pushing of self-ID as helpful or in their own best interests.
Show him the many examples of high-profile left-wingers who are prominent examples of GC feminists, and ask if he thinks they have all suddenly become right wing.
And if none of that works, switch his internet off until his critical thinking skills have caught up with his surety of always being right!