From what I understand reservations are separate from the interrail pass but you can make the reservations and pay for the reservation for the specific train time you want to take on the interrail website.
You can in fact make reservations in many places (websites, ticket offices, by phone, ...), including on the Interrail website. Options depend on the train to book.
But when you make the reservation, do you have to print it out and show it on the train along with the QR code on your interrail app or can you put the reservation you have bought on the app?
If it's a mandatory reservation, just have it ready to show for ticket inspection, along with the QR code.
You don't have to print it, unless it's for a night train, in which case it's a good idea to print it. You can't put reservations in the app (that wouldn't work with paper reservations bought at the ticket office anyway).
Varies per country/railway but in general NO and certainly not in FR-well over 50% of pax will have it on their fone. In most cases on the starting point of a TGV there are manmade fences or checks-and sometimes now gates, where you have to scan this to gain access (and till a few monthes ago the covid-passes were also checked there-that is no more). The aim of this is to bar people who do not have any right to use that train from the platform. Most often there are no more checks on board then. IF there are-it all depends on mood and education of the conductor what s/he wants to see.
IF you do the REServ on the machines (a good way-and reliable enough for a few days advance for INland only)-then you get a long printed slip of paper with a QR code now.
(yesterday eve I used an overnite=nonTGV and there were no checks at all on board for >7 hrs.-at the end they came but then there was a kind of alarm so they had to see at that first.
So I can just show them the reservation on my phone and not have to print it out?
