Hi there! I need recommendation on which panoramic train/(s) to choose from in Switzerland as eurail holders (travelling at 23-26 July): here is our rough planned itinerary for now (the one colored blue are the one we’re going to activate our eurail passes)

The one trip i am most indecisive with panoramic train i think would be our last trip from interlaken to Venezia Mestre. I’m considering this routes:
- Interlaken - Lucerne (Zentralbahn) reservation optional, 16 euro
- then followed by Lucerne > Bellinzona > Milan Central > Venezia Mestre
- St. Moritz - Tirano (Bernina Express) reservation 33 euro
- then followed by Tirano - Colico > Milan Central > Venezia Mestre
my questions are:
- I heard the Zentralbahn route is also really nice with the Lake Brienz view. So is Bernina Express worth it for that price to hop on in summer? (will we pass through icy glacier alps and snowy panorama? We are from tropical country so snowy panorama would be very nice. We’re okay with spending a bit more as long as the price is still reasonable and it is indeed worth it.
- In interrail, we can’t find the trip from Tirano to Mestre Venezia. The whole trip only shows Not in Pass Network, although TrenItalia has it already (Tirano > Milan Centraal > Mestre) . Can we just make our own route? But i’m not sure if it requires reservation or no? and is it really covered with interrail?
- Looking at other days on my itinerary, are there any other possible panoramic train routes that is worth hopping on to? Maybe Glacier Express or others? If the reservation seat is covered by eurail it would be a lot nicer. I really want to try seeing the Belle Epoque train but not sure in which route/day i can fit that into
for consideration: we’re thinking of just paying extra for one really nice panoramic train, and maybe additional shorter panoramic train that requires no reservation fee.
Any help would be appreciatedd