My mistake. I didn’t examine the error message you provided closely enough.
My only guesses then are that the module isn’t available in the version of the kernel you are trying to install (unlikely, but you might try something like “find /lib/modules/5.6.19-300.fc32.x86_64 -name ‘lz4*’” to be sure). Or maybe that the module name isn’t being passed right. I’ve seen the latter occur when, e.g., add_drivers+=“zfs” is used in one config file and add_drivers+=“nfs” is in another config file. Dracut ends up trying to add “nfszfs” to the initramfs which, of course, doesn’t exist. If you look closely at the documentation, you will see that there are supposed to be spaces between the quotes and the module name (i.e. add_drivers+=" zfs “). That leads to another idea though. Are there supposed to be multiple -m flags? What if you specified add_drivers+=” lz4 " and add_drivers+=" lz4_compress " as separate line items?
That’s all I know. Sorry.