Appears that I have encountered this problem as well. Running kernel is 4.19.0-0.bpo.4-rt-amd64, which is the only installed kernel, relevant kernel headers are also installed (and are the only headers packages).
# dpkg -l 'linux-headers-*' 'linux-image-*' Desired=Unknown/Install/Remove/Purge/Hold | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) ||/ Name Version Architecture Description +++-========================-=================-=================-===================================================== ii linux-headers-4.19.0-0.b 4.19.28-2~bpo9+1 all Common header files for Linux 4.19.0-0.bpo.4-rt ii linux-headers-4.19.0-0.b 4.19.28-2~bpo9+1 amd64 Header files for Linux 4.19.0-0.bpo.4-rt-amd64 ii linux-image-4.19.0-0.bpo 4.19.28-2~bpo9+1 amd64 Linux 4.19 for 64-bit PCs, PREEMPT_RT (signed) # modprobe -v wireguard insmod /lib/modules/4.19.0-0.bpo.4-rt-amd64/updates/dkms/wireguard.ko modprobe: ERROR: could not insert 'wireguard': Exec format error # dmesg | tail -1 [omitted] module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 1, loc 000 0000072e61b9a, val ffffffffc0cb8896
