I finally figured out part of it. I didn't realize that the button I clicked was a means to download the file. I thought when you told me to download it, I'd need to know where to get it from.
When I finally figured that part out, the next issue was, my downloads don't go to ~/Downloads. They go instead to /mnt/Downloads/Linux. I found it there. But when I tried to install it from there, its dependencies couldn't be found.
root@malachite-solus-4-2-plasma /mnt/Downloads/Linux # eopkg it bluez-5.60-34-1-x86_64.eopkg
System error. Program terminated.
External dependencies not satisfied: glibc release >= 67
Please use 'eopkg help' for general help.
Use --debug to see a traceback.
Apparently my glibc has never been updated, although I've done complete upgrades every time.
Where should I copy that .eopkg file to, in order to get it to install?