[Custom Audience] How to create a custom Audience from users ID?

Hi There,

Could you tell me if it's still possible, and if so how, to create a custom audience on Facebook using user ID ?

If not, do you have some tricks that work to transform those users id into something targetable ? (idk, like maybe using the old @Facebook email or something could still work for custom audiences, this kind of hacks)

Thank you ! :)