I created an alphabet directly via illustrator ( v 27.4 ) working from a mac desktop. I tried importing A-Z and then one letter at a time. In all cases the letter(s) appears in the lower menu but in the preview area. i i only get one rectangle with an x through it. below the letter in the lower menu I get an x on an orange background. i saved to system font folder and see the font name.otf. when i try and add letters in illustrator each letter is a rectangle with an x through it on an orange background.
i restarted illustrator and the computer. i’m running macos ( v 12.5 )
You must switch back the glyphs name option from Unicode to Character on the bottom left panel. Then just select the orange box and type the exact character key to assign it.