My understanding [1] is that Google Analytics gender data is dependent on user-supplied info which may or may not be accurate, depending on whether the user chooses to supply their real name, real age, and real gender.
There are advantages to having internet advertisers think you're male instead of female. I got tired of all the ridiculous stereotypical makeup ads and haircare ads and fashion/clothing ads and other foolishness - not all women have need for that type of nonsense and I found it insulting that they'd think I would just based on gender.
So when I signed up for one of my Gmail accounts years ago I intentionally gave them the wrong gender (and a fake name as well) to see if the targeted advertising would change.
Yep, sure enough, once they thought I was male they started showing new-car ads and higher-education ads... and ads for those pills which I definitely don't need.
Nowadays I use ad blockers, so I don't care what useless products the advertisers think I want because I don't have to see any of their ads anymore. I'm not motivated to go check various sites' settings to see if they're real-world accurate. I don't do Facebook or any of that, so there aren't any issues with being misidentified among friends; if I want to talk with friends (real ones, not imitation friends online) we use the phone or text or do old-fashioned visits. Many of the people I know don't have internet nor smartphones anyway (yeah, we still exist, we're not entirely extinct yet).
Until such future time when internet usage may require providing official state-issued picture ID with all the personal info included, one would suspect that the various current online analytics are not necessarily a particularly accurate reflection of reality.
Of course, meanwhile, there are ever-increasing methods of data-slurping and data sharing/selling and various forms of 'privacy' invasion etc, so nothing is ever really 'secure' or private. But still at this point I wouldn't necessarily believe everything that Google Analytics says.
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Footnote:
1. Based on stuff I've read over the years, such as this StackExchange ProWebmasters article titled "How does Google Analytics know the sex, age, interests of visitors?" If you use a fake name, fake DOB, wrong gender, don't do Facebook etc, they may not know the difference nor care... yet.
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