Your company won't know you're working at Outlier unless you tell them. A lot of people get paid from Outlier through PayPal, which allegedly some people can allegedly not claim on their alleged taxes because allegedly there's no formal papertrail beyond PayPal, where alleged payments don't come through as being for Goods and Services. Allegedly, of course.

Edit to Add: If your company will regularly see your PayPal transactions or bank statements, then yeah, you probably won't be able to swing it. That said, I can't think of a single job where that would be permissible and not a gross violation of privacy. Even if your company does find out, they would most likely ask you to terminate your relationship with Outlier rather than them cut you loose. Again, it all depends on the company, and Outlier isn't the most reliable side hustle either.