Not a single argument, but I find it interesting how often TRAs contradict each other. For example:

In our LGB definition sexuality depends on sex. Gay men want men of the male sex.

For them, initially, gender is all. The way you identify is the most important thing and defines also your placement in relation to people's sexualities. So if you identify as man, you're a man. In this definition, gay men want men - and everyone who identifies as man fits this.

This leaves large gaps in a TRA mindset, but maybe the largest gap has the non-binary shape. After all, non-binary people (and other neo-gender identities) don't identify as man. So now gay men want masculinity - everyone who performs masculinity fits this, regardless of identifying as man.

Obviously this invalidates men who aren't masculine enough. Ironically, it even invalidates non-masculine transmen.

There are more versions of this "gay men don't feel attracted to genitals, they actually feel attracted to X" argument, and they all keep contradicting each other. But these 2 are the ones I remember right now. Feel free to reply adding more of these arguments that you might have heard!