So I’m looking at themes from GnomeLook, and stumbling upon how to install and use.
I do have user themes turned on through the extensions.gnome.org page.
I’ve put the extracted files in both .Themes and /usr/share/themes
Tried removing yast branding.
Running Leap 15.1
I guess I’m expecting to see these via a dropdown in the Gnome Tweak tool, and they’re just not there, and at a loss as to what to do next. Thanks
Hi and welcome to the Forum 
The $HOME directory needs to be .themes not .Themes, same goes for any icons (.icons) and fonts (.fonts).
Remove them from /usr/share/themes
Where did you get the themes from? Can you post a link?
Yes, once the user-themes extension is installed, then you will see in the Tweaks Tool.
Now, how did you extract the tarball, sometimes the create a lower directory, it does need to just be in ~/.themes eg;
ll .themes/
..
...
drwxr-xr-x 3 username users 25 Feb 23 2017 Gnome-OSX-IV-Dark-Shell