Merry Christmas !
To install a new font you can simply put it in the system Fonts (not the user) folder -> /Library/Fonts/
This is where all your system libraries are installed.
The font file must be in ttf format, this is maybe some of your fonts are not displayed (or a matter of character set supported by the font).
If you don't have your font in the ttf format, say you have it in otf, there are a lot of converter on the web.
Like this one: https://everythingfonts.com/otf-to-ttf
We could list the user library folder as well, i will add that to our wish list.