The Golden Pass rail route:
Current tourist branding can be confusing
The true Goldenpass is just the MOB railway Zweisimmen - Montreux.
The Luzern - Interlaken railway is actually the Brünig Pass line operated by Zentralbahn (ZB), which dubs the regular trains "Luzern - Interlaken Express'. It's OK but not spectacular scenery
A few facts about the Montreux - Zweisimmen railway - ie the MOB (Montreux-Oberland - Bernois):
The Golden Pass is historically only Montreux - Zweisimmen, only more recent marketing branding takes the 'Goldenpass route' east of Zweisimmen to Interlaken and beyond to Luzern.
The Golden Pass is the touristic branding for the Montreux - Oberland Bernois (MOB) railway
MOB pioneered the Panoramic coach concept on Swiss trains, starting in 1976.
There are now several versions of panoramic coaches in service, but MOB keeps changing its mind how to dub each service.
It hardly matters anyway as most modern Swiss trains have large windows, even if not officially panoramic. The key element of a ‘panoramic’ coach is ‘toplight’ windows above your head but in practice very few of the major views from panoramic trains are directly above your head, so the view through the normal side part of windows is normally fine.
You will get roughly the same scenic experience form any train on the MOB and reservation is not obligatory
Here is the timetable PDF for the MOB:
www.fahrplanfelder.ch/ fileadmin/fap_pdf_fiel ds/2019/120.pdf
It is very scenic, but the MOB route is far from being the most spectacular (although any dubbing of this nature is going to subjective and personal) in Switzerland.