My biggest concern would be the screw jack post.
Those are designed for temporary support and this one is picking up the load of the hearth concrete slab. If I am not mistaken, your third pic seems to indicate a sag in the joist.
The post was positioned there most likely to supplement the single joist that are picking up the floor load from the header. Those floor joist should have been double if not triple depending on the span.
I would refer to an SE on this one to get it evaluated.
I also noticed you could hang clothes hangers on the electrical wiring and an open box. Couldn’t resist:twisted: