I don't see a fix in the link, we still know that your window size is 1280x923 and that you started your search with "ran online" and then added "ran online gameplay" etc...
The hard truth is: Anyone who has to ask this question does not have enough experience in programming. If you're unable to simply guess what the boundaries of a game you want to make are and what technology is involved, you're not ready to approach such a game in general.
Here are two other source that might help understand what you're up against:
#1 #2If you want a direct answer instead: Yes, SFML can be used to make an MMORPG.