When we start “Anonymize past data” , we always stay in the "In progress" Status (even after days).
We tried manually from the Matomo backend and also with the command line.
Do you get any error when you execute it on the command line? Can you paste the output here?
If your DB is very large, it could take a VERY long time for such a big date range (depending when you started tracking data and how much data is in there). Maybe check your processlist if the command is maybe still running or so? You might also need to use something like
nohup to keep the command active after you log out via ssh...