google-noto-sans-cjk-fonts and google-noto-serif-cjk-fonts switched to variable
fonts, but some applications don't support it well.

For the following two examples, assume the font "Noto Sans CJK JP" is installed
as a variable font.

JDownloader (installed by flatpak):
1. Open Settings from the menu
2. Select Advanced Settings in the left panel
3. enter "font name" in the textbox to filter the settings
4. enter Noto Sans CJK JP in the value field
5. Restart JDownloader
6. The new characters are too thin. It seems like it's using the smallest
weight. And there is no way to select other weights.

Freeplane (from repo
http://download.opensuse.org/repositories/Office/openSUSE_Tumbleweed/):
1. Select Noto Sans CJK JP by the pulldown menu in the the toolbar
2. The characters in nodes are very thin

For static fonts, all weights are installed as separate fonts and can be
selected in the UI of the applications.

I think giving users the option to install static fonts instead is more
feasible than identifying all those applications incompatible with variable
fonts and have them support it.