3rd party logos
Logos, like any other images, are complicated and can have a variety of “correct” answers for being accessible.
Company logos do not need to meet accessibility criterion per WCAG 1.4. 3 ("Text that is part of a logo or brand name has no contrast requirement").
However, if you have flexibility with the logo design and can make it pass contrast guidelines, that's a great thing to do.
Summary:
Use appropriate alt text
use appropriate focus state (if contained within a link)
don't worry about size
don't worry about color contrast
don't worry about scalability
don't worry about hover states
Include alt text for every important logo/image
Alt text describes images to visitors who are unable to see them. This includes screen readers and browsers that block images, but it also includes users who are sight-impaired or otherwise unable to visually identify an image.
Decorative images:
Images/logos that are not necessary for comprehending or engaging with the content are considered decorative. Decorative images/logos should be marked as decorative or screen readers will guess a description, usually speaking aloud a sometimes cumbersome filename like “hero-image_293_version_953”.
See W3’s alt text decision tree to help determine whether an image is decorative.
Refer to the icon component under accessibility tab for more: Icon
