A tricky question for me. My starting point is that the oppression of women and girls is sex-based at its root, and that feminist activism should therefore prioritise fighting sex-based discrimination, sexism, sexual violence against women and girls, and the still common view that the female sex is simply the inferior sex.
Transmen are female, so in that sense many of the difficulties they face will be about sex-based issues, but those transmen who pass will reap male privilege (the average earnings of transmen rise after transitioning, though not much). Yet they still have female reproductive systems and might face sex-based obstacles in that field. Clearly, feminism would also benefit them if it gets/keeps abortion legalised etc. But they could also benefit from some anti-feminist policies that out-of-closet-wombcarriers will not.
The big problem I have is with those transmen who have openly excluded themselves from the sex class which used to be called women, and who insist that the new identity class 'women' should consist of only individuals who are feminine, i.e., submissive, passive, emotional and nurturing, which they are not. This turns my sex class and my embodied identity into sexist caricatures.
So those activists in this group (and many, many nonbinary-identifying female people) in my opinion are doing damage to feminism and the vast majority of women and girls by trying to erase our embodied identities and by making what looks to me like private contracts with the 'patriarchy' to both get all the benefits from feminism (repro rights for 'uterus-havers') and to escape being treated with sexism and misogyny.
That they seem to treat me and other bog-standard women with some contempt hurts and angers me. At the same time, they remain female, and in that sense my feminism would also cover their sex-based mistreatment. But I would not go out of my way to erase my own identity to include them in some group they have voluntarily first left.