Hi Asher S Einhorn,
Jump is a function that is part of the character class that is defined in the engine’s source code. All of the other functions listed in the overridable section are events, which react to a certain thing and then activate instead of actually executing any code. This is why it cannot be overriden through blueprints. If you wish to override it for use in blueprint, you would need to get the source code version of the engine and you would have to do so using C++.
Otherwise, I would suggest, if you wish to make a jump function of your own, calling it a different name to avoid this error. As for actually making one, you should be able to get quite a few ideas from this post: Is there a way to stimulate jumping using Blueprint? - Blueprint - Epic Developer Community Forums
Hope this answers your question. Have a nice day.