He's also doing some conferences during the day (on the 21st at Rosewood Amsterdam, time unknown and the 22nd at Felix Meritis (Zuilenzaal), also time unknown). You might want to try to wait there too, but like I said: the times for these are still unknown but they are during the day and I don't know how it works with artist entrances there.
Don't bother attending these conferences since it'll cost you 725 euros for a Pro pass ticket ;-(
I remember in 2019 when we (user 1906 and me) were waiting for our train and we saw JMJ and Fiona at the same platform waiting for their hi speed train to Paris.

So it's also a bit of luck.