Virtual museums and digital exhibits are nearly interchangeable, and depending who you ask, they might be the same thing. However, one can scrutinize some differences- namely that virtual museums are broader in scope and often more sophisticated. A virtual museum can also contain or showcase a digital exhibit. For example, The Getty museum in Los Angeles is a general art museum, but it highlights specific exhibits on 19th century Danish art, Ancient Iraq palace art, Michelangelo, etc. In fact, some real museums will have host virtual versions of themselves, while others are born digital and only exist in the virtual realm.
Virtual Museums are more comprehensive, yet still exist within the virtual realm. They often use Virtual Reality and Augmented Reality in their spaces, provide virtual tours to the patrons, and focus on the broader theme as a whole.
Digital exhibits are typically designed and curated much like real exhibits in that they still aspire to emphasis specific themes or topics and to educate the "patron", but with the emphasis on digital content. Digital exhibits often provide the "patron" with interactive content like slideshows and 3D models of objects.
It should be noted that in addition to the desire of wanting to provide users with more equitable access to information, Covid was also a huge proponent in propelling this type of virtual exhibition(s).