SYD-LHR would usually be booked as a single segment on either BA (as BA 16) or on QF (as QF 1), even though in either case it is a single direct flight comprising two legs.

If there is a list of multileg flights, I do not know of it.

If you mean is there a list of two-segment flights equivalent to a single segment flight (like BA 16 SYDSIN, followed by BA 12 SINLHR is very similar to BA 16 SINLHR with a stop in SIN), I would doubt this exists.

However if you have some specific journey in mind, I am sure the collective wisdom here will be able to answer your question.