Not sure about the numbers, but the trains I’ve used yesterday in the Netherlands seemed quite well filled and stations busy considering we are still in lockdown. Each bay of 4 had at least a person in them and all airline seats also had one person in them. But this was off-peak, in the peaks I think the largest decrease is.
Especially in the weekends the trains are indeed quite busy in The Netherlands now, but at weekdays I'm usually seeing pretty empty trains (as far as I can look inside when changing from bus to bike at Veenendaal-De Klomp station on my daily commute, lucky me that I can't work from home).
Although trains can also just look busy because they're shorter, there are quite a lot of services which used to run with 12-car double decker sets which are now running with a single four car unit.
In general the number of check-ins in Dutch public transport (all, so including buses, trams and metro) is at 30% of 2019-levels at the moment. Rail usage has also dropped again now we are in the second lockdown, I believe I've once read it was at 75% of 2019 level during weekends at the end of summer. NS was already mentioning back then that they recreative travel had recovered much quicker than the number of commuters.
What the future will bring is still a big question mark. Clarity has not been given yet by the government if supportive funding will continue after October and province after province is now sounding the alarm bells as they might have to cut up to 30% of all public transport. That would partially also hit rail transport as the provinces Zuid-Holland, Limburg, Gelderland, Overijssel, Drenthe, Groningen and Friesland also are resposible for several regional railway lines.
In the mean time NS is also investing in marketing to reassure the public they will be there to transport them whenever it's allowed again...