The Chicago Manual of Style does a good job of providing examples of citing different kinds of social media platforms.
The online version of MLA provides guidance in a few different sections:
- See 2.107 for titles of apps (put in italics, e.g. Instagram, TikTok)
- see 2.123 on very long titles (see note about social media posts)
- Sections 5.31-5.37 speak about Containers: e.g. how to cite a photo or video clip included on Instagram, TikTok, etc.