Another noob X file:

I can't set ":weight Light" for a font.

If I set it using the "Menu, Options, Set Default font, Cascadia Mono - style Light"; the text in the buffer changes correctly;

but in the init.el the :family changes into "Cascadia Mono Light".

When restarting, it seems that family "Cascadia Mono Light" doesn't exist, so the default font family changes by itself into "Frank Ruhl Hofshi".

In the customization buffer family is "Frank Ruhl Hofshi",

but in the init.el family is "Cascadia Mono Light".

If I set in the customization buffer (:family Cascadia Mono :weight light) the default font in the buffers doesn't acquire the :weight light.

In the init.el it appears :family "Cascadia Mono" :weight light.

In the customization buffer weight goes back to "normal".

Could it be related with light and Light capitalization?

Could it be some kind of curse for using a non free font?