The %OAuth2.Server.Generate is the default GenerateTokernClass which is included with the server.
The default class will generate a random string as the opaque access token.
The GenerateTokenClass is specified in the Authorization Server Configuration. It must contain a GenerateAccessToken method will be used to generate an access token based on the array of properties that is returned by the ValidateUser method.
The GenerateAccessToken method returns an access token. The access token may be based on the properties argument. In addition values for claims to be added to the JSON response object may be returned in the properties.ResponseProperties array. classmethod IsJWT() as %Boolean
However the method in this default class just returns an opaque random string.
The IsJWT method returns true if the GenerateAccessToken method returns a JWT. IsJWT is used to determine inclusion of algorithms for access token in server metadata.