Can an LLC be a non-profits? Or are LLC's by definition for-profit organizations? If the former, how would that designation be reached?
An LLC can obtain a 501(c)(3) designation, but all its members/owners must also be 501(c)(3) non-profits.
So if Red Cross and Habitat for Humanity and Goodwill got together to start an LLC, that LLC could obtain a 501(c)(3) designation. If a human person is a member of an LLC, that LLC cannot obtain a 501(c)(3) designation.
I don't think there's any reason a for-profit LLC could not accept donations from Patreon or Kickstarter, but those donations would generally be treated as income, the same as money received in exchange for goods.