I hear this "a lot" very often, but then it seems to be from people who have no real interest in technical work of kernel/OS core development. Linux is not the only way to scratch your itch for interest in low-level system dev. Like, this is just personal experience, but I have heard this on the order of 50-100 times: someone parroting how toxic Linux kernel dev is because of drama they heard -- but then you kind of dig a little bit and see what kinds of software stuff interests them, what do they work on -- probably only once or twice has it been anything embedded, hardware related, close to the metal. I would need compelling evidence to change my opinion that most of the complainers have no interest in the work being done by the community they are complaining about -- and I am fully aware that a number of people have departed Linux development, but we are talking about a tiny number of the thousands of contributors over the years -- you can't please everyone.
The hobby OS, emulation and demo scene is a pretty good indicator for "natural"* gender breakdown. These tend to be tight, tiny communities or often lone wolves working on projects. It is male dominated. This can't be explained by any systemic or community gatekeeping - because there is no system nor any mandatory community for participation or distribution. Nothing prevents anyone from putting their work out there.
* I am not discounting there may be other systemic reasons that set up this condition - but it has to be societal conditions that are in place in early childhood -- something that happens a bit before one considers contributing to the Linux kernel.