Answer by Kamil Maciorowski for Is there a quick way to reclaim space overallocated for files on ext4?

Is there a better way to clean it up than writing a script with truncate and running it over the whole system?

Write a short command with truncate and run it over whatever you want. This example will try to apply truncate -s +0 to regular files in the current working directory and below.

find . -type f -exec truncate -s +0 {} +

(Append -print to see pathnames.)