While I prefer etresoft's response, I'll add on anyway.
This is precisely the PingFang True Type collection containing the MO subset I wanted to install manually offline and NOT as a downloadable.
You can't use that font. Period. It isn't even a complete font. It's pointless to even try and use it. You can download the FULL versions of the MO fonts via Font Book. Surely, this cannot be difficult to understand.

Downloadables are deactivated automatically by Apple without user's consent.
I'm not sure which alien species told you that, but they are about a bazillion percent wrong. Every font you can choose to download is set up that way because a) the OS doesn't need them for language support, and b) most people (non Asian users) have no use for these. So it's a waste of drive space to install fonts you will likely never use. But they are there to download if you need them.
And no, Apple cannot, and does not somehow remotely control them. Once downloaded and on your Mac, you can disable or enable them anytime you like, just as you do any other fonts.
In short the Downloadables menu should display the «No downloadable fonts available» message once the fonts are permanently installed in the Fonts directory, allowing for manual activation/deactivation without the need to redownload them.
Where are you finding this nonsense? Once downloaded, they're on your Mac until you choose to remove them. They do not need to be downloaded each time you need to use them.