Here's an article (in German) from last year where Richard Lutz, boss at the time of Deutsche Bahn, says they needed at least twice as much as what they were getting:

https://www.tagesspiegel.de/wirtschaft/mobilitaet/trotz-sond...

And here's an article (also in German) from this year about how the money that's been promised is not being delivered, leading to the cancelation of 90 projects.

https://www.tagesspiegel.de/politik/es-fehlt-das-geld-mehr-a...

I also remember an article about how part of the train budget was being redistributed to fix highways, but I can't find it right now.

So I agree with the parent comment: the current investment is not enough and what little they have is constantly being diverted.