Checking the OBB site shows one connection to be:
1. Salzburg Hbf (14:08) to Wien Westbanhof (16:30)
What's the date? Since it's a bit weird to start as early as 14:08 when your flight is at 22:30. Line Salzburg-Vienna has very frequent traffic (OeBB Austrian State Railways and WestBahn private company), so you should easily be able to start in between 16-17 and be in Vienna on time
2. walk 166m to Wien Westbanhof U3 (is this easy to navigate?)
3. Wien Westbanhof U3 (16:38) to Erdberg U3 (16:52)
4. Erdberg U3 (16:52) to Erdberg VIB Platform 3 (17:00) (what does this mean? we walk from U3 platform to VIB platform 3?)
5. walk from Erdberg VIB to Flughafen Wien Bus Terminal, 59m. (will be be easy signposting for commuters to follow? what to watch out for here?)
6. Take Bus 6000 to reach VIE in 15 mins time. (how far will the bus terminal be from the International departure hall?)
To be honest, it is way too complicated. Route planners time to time tend to propose such multiple change journeys in order to save like 5 or 10 minutes in total travel time. We find it not worth the hassle, especially for people not well acquainted with Vienna city transport system, much easier will be just to catch train from Salzburg to Wien Westbahnhof and then take direct
airport bus from there (bus stop is just in front of the train station), which will take you to airport bus station (located in front of arrivals hall, but it's
very easy to get form there to departure) E.g. depart from Salzburg 16:08, arr. to Wien West 18:30 and catch 18:40 bus to the airport (arr. 19:25)
Also remember that in case you departure date is not in the next few days, in advance train ticket purchase can actually save you quite a lot of money on OeBB tickets. Or alternatively, you can just use
WestBahn and pay only 24,9 euro (compared to 50+ euro for OeBB full fare standard ticket)