The data is misleading at best, probably manipulated. Let’s not forget the data is from DB itself.

As an example, in 2018, the then boss of infra at DB, Ronald Pofalla introduced the “Pofalla Wende”, whereby a commuting train between two cities will simply turn around and not serve the rest of the line if it has a certain delay. In itself, one could argue it can make sense under certain circumstances. But all remaining stations on the line are not counted as delays, even if there is not replacement train.

Same with cancellations, these don’t show up as delays.

The situation is significantly more dire than what this data shows.

COVID harmed most industries that rely on manual labor. Suggested reasons vary, one is that people discovered they could do mental-work, and preferred it (and apparently it never occurred to them before). Another reason is many retirements and a gap in knowledge transfer to the next generation. Another is a huge increase in demand for non-physical work during COVID that never went away, leaving other industries short handed (and it's not a pay thing, there's not enough people for all demand in all industries, someone must run short).

Maybe the DB staff went soft during the lockdowns. Maybe some employees left and institutional knowledge suffered. The same thing happened with the truck driver shortage.

The way neoliberalism dealt with the public sector including rail service and infrastructure and then come up with "COVID killed Deutsche Bahn" is like saying that poor old sucker who was pushed down the staircase succumbed to his running nose. The problems run much deeper and were already visible in the 70s and 80s, but because it's only the public sector and rail traffic, not about more highways and more cars and then even more cars it never got fixed. Because who needs rails and trains, right.

Maybe train personnel out sick?