Cannot find my camera or lens in Filter/Lens Correct. I have a Canon 5D Mark IV. I can only find the Mark III. When I select that and anything that approximates my lens the image changes to fish-eye
Are you shooting raw or jpeg? If you shoot raw, the lens corrections would normally be applied in Camera Raw, not in this filter. If you shoot jpeg, then perhaps there is no jpeg lens profile for the lens you used. Choosing another profile that 'approximates' your lens is useless.