In my DC case, as obviously they approached me and I was at first surprised, they had very definite reasons
This wasn't something done because another mate was doing it.
They are female presenting. They had come out as gay 2 years before. We fully supported this- no reason not to.
Their attitude is women are treated, to put it bluntly, like shit. They feel that all anyone ever sees is female or male. Men are able to do as they wish. Women are placed in two columns- sexy, fit Love Island influencer and thus "worthy and wanted" and everyone else. They said they didn't want to be a body, a vessel of good looking or everything else. That they don't subscribe to female led beliefs and although they also don't feel male, they prefer to be in the middle.
They dress like most teens now in hoody and skinny jeans. They have a short floppy Bob and describe themselves as "alternative". They use the shortened, more associated with masculine version of their feminine name but then, they are named after two family members and both used the more male associated name as a nickname but were and are very much still female.
They were respectful when we hit a bump in that I was getting married and I asked them to be involved, they agreed to be a bridesmaid, with the agreement that at the reception they could get changed into casual clothes- all my bridesmaids did this as it was hot and I didn't wear my wedding dress for long after either
I can accommodate their wishes for as long as this lasts. They've been through some pretty shit times due to the pandemic. Their school has a club for LGBTQ+ where allies are welcome. School is making a safe space for changing for PE ready for next term.
I've explained that in my view, I would rather females in their generation did stuff to make things better for girls rather than declaring themselves neither. That many have already become politically aware and stuff far earlier than my generation did and some kick ass females smashing the patriarchy would be cool. Their attitude was they understood this but felt that it was too much to achieve, too ingrained, too big a task.
Obviously that's my teen, I can't comment for others and their choices. Mermaids is not in their school. School asked me if it was fine to refer to them by their preferred name.
They are happy and as a parent that's all you can hope for, right?