I’m currently unemployed and also, having been on HRT (MtF) for nearly 6 months, I am visibly trans. I, realistically, only still use my legal name for things requiring my legal name to be used.
I’ve been going through the application rigamarole again and I’ve been wondering just how I should go about filling things out. I’m not to the point of full body change yet, but it is passable under a lot of circumstances. Should I still use my legal name on my LinkedIn and when applying for jobs or should I change it to my preferred name?


IANAL, but I would imagine you should use your legal name where it asks for legal name and if it asks for a preferred name, put your preferred name. And once you do legally change your name, you can go to HR to update it.
Good luck!!
There is no legal reason not to use a preferred name, at least in the US.
I got better results when using my preferred name on my resume and cover letters–coincidentally a male-sounding nickname for my given name.