How do I install an old kernel?

You can find a list of all kernels built for Fedora 35 here: (There you can select a kernel and click on Builds).

You can download all kernels that have been built from here:

Then, simply use dnf to install them.

Alternatively, you can use koji download-build -- arch=x86_64 <package-name> to download the package directly, no browsing involved. I would recommend that method.

Here is an example:
1.) mkdir -p kerneldownload
2.) cd kerneldownload
3.) koji download-build --arch=x86_64 kernel-5.16.18-200.fc35
4.) sudo dnf install ./kernel-*