BTFhub, in collaboration with the BTFhub Archive repository, supplies BTF files for all published kernels that lack native support for embedded BTF. This joint effort ensures that even kernels without built-in BTF support can effectively leverage the benefits of eBPF programs, promoting compatibility across various kernel versions.
IIUC, this was accidentally lost in https://github.com/aquasecurity/btfhub/commit/c22ad47e3432e22ed4052b220b12651ab0137433, and caused the BTF for 5.8.18-100.fc31.x86_64.btf to be removed from the archive.