Meaning
A thick, bold plus sign, the symbol for addition in maths. It means add, more, extra or positive, and on many screens it is the button for creating something new.
In chat it adds a person or item to a plan, as in “plus one”, or lists bonuses and perks: “Pizza night at mine ➕ board games after” It is also a quick way to agree and join in, much like replying “me too”. Its opposite is ➖.