There is no real competition for FB, all the users that leave (like I did several years ago) are self-inflicted wounds.
However FB is part of the FAANG group that pays top dollar. That is attracting enough good engineers, especially the type that don't care too much about the ethics of their work results.
FB is not the only large company that pays well. They might pay better than others, but when you're in that income bracket, we're not talking about making ends meet either way. So when you introduce ethics into consideration, it does affect their ability to attract talent.
FWIW their recruiters seem to be getting desperate in the past couple of years. Until then, I'd see a FB recruiter ping me about once every year. But from 2019 on, it's much more frequent, and I know it's not just me - there's many other people I know who have observed that, and you can find more testimonies along those lines in these comments. Furthermore, I have explicitly told them to GFTS in no uncertain terms, and I still got recruiters contacting me after. This tells me that they are feeling the crunch.
However FB is part of the FAANG group that pays top dollar. That is attracting enough good engineers, especially the type that don't care too much about the ethics of their work results.