Is it possible to find a list of all existing Uniform Type Identifiers on a system?
How about
/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -dump
Even better: A Graph of all Universal Type Identifiers - Kevin Ballard's Blog
Full list of UTI types is available here https://developer.apple.com/library/archive/documentation/Miscellaneous/Reference/UTIRef/Articles/System-DeclaredUniformTypeIdentifiers.html#//apple_ref/doc/uid/TP40009259-SW1
You can build your own graph with UTIsExplorer https://github.com/nst/UTIsExplorer
The project includes a graph of all UTIs on my machine: http://seriot.ch/resources/utis_graph/utis_graph.pdf