Gender bias in advertising
There are a few things going on here. The actual case seems pretty clear cut even with only my limited understanding of employment law. Business students in the EU are expected to be aware of US employment law :)
Firstly, if it's illegal to only advertise a job to one gender, then "target only male/female" shouldn't be an option for job ads. Same for all the other rules about what you can and can't bias against (ie only targeting ads at people with a STEM degree is probably OK).
The more fuzzy problem is that even without explicitly excluding women from the advertising pool, women will (generally) be shown less of the ad anyway. Because Facebook (and google et al) charges more for a woman's ad impression than a man's. That's not artificial either, advertisers pay more because there is more demand for it.
This effect doubles down for professional women, as they have more disposable income, so they are even more expensive to buy impressions for.
Thus you can get a gender bias in job ad impressions without any "girls can't do it" crap, just because other people will pay more to get those eyeballs.
As for women in the workforce, my overwhelming impression has been that they are generally harder working, paid less and much more adapt at reducing social friction. Obviously many exceptions abound, this being humanity and all. But the best sysadmin, change control, problem management, mechanic/inventor and IT managers I've known have been all been women.