the icon not show

Hi, please help me to show icon at my homepage, I was setting on customize theme, Homepage section> Service section, Service Icon can’t “fa-brands fa-themeisle”.

If I insert “fa-brands fa-themeisle”. its tobe one word: fa-brandsfa-themeisle. and if I insert “fa-themeisle” its not show.

that only can use fa-regular without fa-regular, may if i want use “fa-regular fa-web-awesome”, i just insert “fa-web-awesome”. it show.

Please help to may be if I want to show used fa-solid, fa-brand, fa-light, fa-duotone, etc.

Thanks before for your help.