/lib/modules/$(uname -r)

At least Debian seems to install kernel modules not directly under /lib/modules but in a «versioned» sub-directory named after the result of uname -r.

The Debian/APT package linux-image-$(uname -r) contains some of the files located in this directory.

Compare with the APT package linux-headers-$(uname -r).

/usr/src/linux-headers-$(uname -r)