They can be feminist allies but never a feminist. There are plenty of reasons, too many to list. Here are a few main reasons,

They never experienced what women experienced. They are biologically different. They often think about their own gains, but selfishness is a tool of survival of the fittest and natural selection, all humans are selfish. That is a major reason they cannot be a feminist.

Trust issues are the number 1 obstacle from accepting males as feminists, it's difficult to accept a male as an ally, even harder to accept a male as a feminist.The word feminism comes from feminine and ism. It's female centric. There are no rules and laws to govern what a male feminist can or cannot do. We need a sovereign state / land for that.

Feminism is a lifestyle, you cannot turn it on or off easily. Males don't have the equipment and social atmosphere to engage in feminist conversations. Women are generally uncomfortable with men when we disagree with them, they might get angry or upset and that makes honest conversations difficult.

Most male feminists expect women to pay half in financial expenses, but women are at disadvantage, males should pay more than half. Male feminists are within a female-centric group, they must agree with female ideas to keep the male feminist label.