Hi @Alex_Blanes - does this give you what you want?
CONCATENATE(IF({Twitter Copy}, "Twitter, ", “”), IF({Facebook Copy}, "Facebook, ", “”))
This concatenates values for each copy column (2 columns in this example - you can extend for 4 copy columns).
The “problem” with this formula is that it forces a comma onto the end of every value even if there is only one value, i.e. "Twitter, ", but maybe this isn’t a problem for you.
Also FYI, you don’t need to have
IF({Twitter Copy} != “”, etc…
But can just have IF({Twitter Copy}
which translates as “if Twitter Copy exists”
Hope this helps!