If some see the emoji (to give them the correct name) but some see squares or blank space, then it’s generally down to font support on the browser and/or OS.
Forum shortcuts where you put the text equivelant will convert to the relevant character, though some forums use their own icons for them. Emojis from your computer / phone get inserted as unicode characters but depends on the font support. If they’re very common ones they’re more likely to be covered by fonts in most browsers. Some rare ones maybe less so. They do tend to render differently on different OS though.
Anyway, Windows 10 shortcut…
Windows Key + ;