So you don't think it could be an old router problem?
So, if I download Mojave or Catalina in my erased Mavericks partition, it will leave Sierra alone and not upgrade it? That's how it works?
What do you mean I can erase it from one of my Sierra volumes? Wouldn't a Sierra volume just have Sierra on it? Do you mean erase it from my internal hard drive and not my external drive? Mavericks is only on my external drive.
I've got no expertise, not even a little bit of amateurise, in routers, but as I see it, the problem is too narrowly defined to be a router issue. Ira just responded negatively in your other post, and joemike, whom I'd call our local expert in this sort of stuff, hasn't contributed, so your router is probably not at issue.
The Mojave and Catalina installers can be run in two ways: they can either upGRADE your Sierra volume or they can do a CLEAN INSTALLATION. You want to do the latter.
Connect your external drive.
Boot into either Sierra volume.
Navigate to /System/Applications/Utilities/Disk Utility.app.
Select the Mavericks partition in DU's sidebar.
Hit "Erase," follow the prompts, and name the newly erased volume either Mojave or Catalina.
Quit Disk Utility.
Download whichever of the OSs you decide to install. (The d/l'ed installer will go to /Applications.)
Launch the installer and follow the prompts to the pane that tells you the default installation destination and offers you an option to change destinations.
Select the volume you just erased and renamed. (You do NOT want to install on either Sierra volume!)
Hit the "Start" button, and when the process is complete you'll have a pristine, vanilla, untouched by human hands installation.
Try Amazon.
Report success.
I think that answers all of your questions.
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