There seem to be currently 11 of them in mid 2023. https://www.flightradar24.com/blog/where-can-you-catch-a-747-400-in-2023/

If an airline has one or two as a back-up but it does fewer than 1 flight per week, it does not count as regular passenger service.

Where can you catch a 747-400 in 2023? | Flightradar24 Blog

Want to know where to catch a Boeing 747-400 in 2023? They’re on the decline but still out there. Here’s a look at the data.