That specific link is to a x86 package. If you have a smaller arm nas, you need to find the correct version.
Then you need to extract the zip file to get the spk file to install. Should just install through the web GUI then.
However, I have found the newer releases of those packages to not work properly. Segmentation faults on multiple releases. This might be specific to the antique NAS I’m using, or perhaps it’s specific CPU, or maybe the DSM version, but the symptoms listed in the original post sound like the same thing - it doesn’t start because it just crashes immediately.
I think I figured it out. OSX is so clevar it hid from me that the .zip file contained a .spk and just opened the spk and showed me a folder with random stuff that didn’t look installable.