Is it permissible to accept financial compensation from an American company for displaying its advertisements on a device, knowing that the company engages in both permissible and impermissible activities, and that the viewer is not required to watch the advertisements or visit the advertised websites? And would this be considered cooperation in sin if others were to watch them?

The ruling on the prohibition of money earned from a forbidden advertisement does not change, whether you are aware of its content or not, or whether you publish it or not. This is because merely granting permission to the company to display its forbidden advertisement on your device is impermissible. The money earned from it is unlawful because it is in exchange for a forbidden benefit. This falls under cooperating in sin, and publishing the advertisement further increases the sin.