Comments here about miniature and tourism tagging are all good and true. There really are differences between rail that is “out in the public across vast distances” and that which is more isolated, perhaps in a park or theme park, and doesn’t really “go anywhere,” except to entertain or perhaps educate on the history of the rail, maybe associated with a rail museum.
My approach to these (and the tagging I use and has emerged in OSM over a decade or two) is that “rail that people can ride” are quite different from each other, falling into roughly three kinds. (I purposely exclude freight, industrial, military and scientific rail here, as those do not convey passengers):
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There is “passenger rail” of the sort that ranges from long-distance international and national routes (where you might sleep and eat on the train for days, perhaps stretching your legs at brief stops at stations along the way), medium-distance “regional” or “intercity” rail (where you might spend many hours or most of a day going from city to city), “suburban” rail of the sort that commuters might ride for most of an hour to and from work, “city” or “light” rail, a higher-caliber, tram-like, moderate speed (not slow, like trams or purely local rail) passenger service that spans (and may or may not fully cover) larger cities with one, two, three or more different lines, and more “local” passenger rail service which can include trams, streetcars, cable cars and other short-distance rail that is designed to offer point-to-point passenger transport services. Local can also include things like airport-style “terminal-to-terminal” rail, or short-distance monorails, though not in theme parks.
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There is “tourist rail” which often results from “keeping alive” a rail line which decades (or a century) ago was a real, working industrial / freight rail but now has been converted to a tourist attraction or part of a rail museum experience. It doesn’t really “go anywhere” but is both enjoyable and educational to ride. Sometimes (rarely, really), this can offer a modicum of “local service” from point-to-point, but that usually isn’t the primary reason for such rail: it is primarily tourism-oriented.
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Also tourism-oriented, but in a different way, there are either “theme park” rail (at places like Disneyland or Disneyworld) or “miniature” rail (it may also be “full scale” or “standard gauge” rail) or monorail at places like city parks, county fairgrounds, private ranches and the like. These are also “tourism oriented,” but are not part of a theme park experience, but rather are a single passenger rail experience specific to that location.
Respectively (at least as consensus has emerged in California and more widely, in the USA), these get tags passenger=international, passenger=national, passenger=regional, passenger=suburban, passenger=urban and passenger=local. That last tag is rather broad and needs some discretion in its tagging.
See California/Railroads/Passenger - OpenStreetMap Wiki (and perhaps its associated parent- and sub-wikis) for an example of a catalog of these various kinds of passenger rail, how we categorize them and how we tag them. The section of this wiki — Section 2, " Tourism, museum, heritage and historic (possibly passenger=local trains)" — which includes tables that contain “theme park” rail entries might help you converge those examples with your specific kinds of “theme park passenger rail.”