In broad terms, with such a large city, and a dense level of employment in the central activity area, I suspect that proportionally more people commute to central London by rail than commute to central Vienna / Graz / Salzburg / etc by rail.
Many more of these daily commuters are travelling long distance too (30-150miles // 50-250km), paying £4-10k a year for it, and taking up 2-4 hours of their day. That’s a pretty strong incentive to stop doing so, if you can earn the same money by working at home most of the time.
Then on the ‘push’ side, with central London office rents in the region of £750/Sqm, that’s a strong incentive for employers to downsize and encourage their staff to work at home.
The final point, which is a smaller effect but still worth noting is airport traffic. In 2019 around 2% of GB rail passengers were heading to or from a plane, and that has been slow to recover. It’s also important as it represents rather more than 2% of revenue.