Eurostar is an almost unique exception in that it has check-in times.

Larger Spanish stations have security theatre nonsense so some extra time needs to be allowed for that.

Apart from those examples the time required is precisely how long it takes you to walk from the entrance of the station to the door of the train.

In an unfamiliar large station I would say give yourself 10 minutes to find your train, in most cases you will still have plenty of time to spare.

There are no formal border control checks within the Schengen Zone so no boarding checks at all.

Selamat pagi, mas (yah, ada pagi disini).

On all other trains there is NO check in /whatever-its just that this €* wants to look line an airline-plus that there are the border controls as UK has always been out of common Schengen area. You can in theory arrive till 20 secs before doors close. Once in Schengen common zone=about all of the continent, there are no regular passpt etc checks anymore.

BUT-in some countries-for some trains the stations are gated with barriers-and if youre not familiair with that it may take time to figure out how to pass-plus they also ted to be much larger as KL Sentral=means more time to find platform and train. In Belanda=Nederland all main stations have such gates-some of these should be able to open with QR code on the pass-if not use fone to call assistence-they can open remote.

Gates are also common in FRance-for TGV and in ESpanan-for superfast AVE.

Also awas: by now-due to shortage of stock-most ICE from AMS are limited to Düsseldorf-change there for onward.