The lens to buy for someone who owns a Sony A7 IV
They have the camera and the zoom it came with. This is the next lens.
They have the camera. It came with a zoom, the zoom is perfectly good, and every photograph looks a little like every other photograph.
One small prime lens changes that more than a new camera would. It opens far wider than the zoom, so the background falls away and the face stands out, and it is light enough that it stays on the camera instead of in a drawer.
So the answer is
Sony FE 50mm f/1.8
Small, light, and the cheapest way to get the soft blurred background people mean when they say a photograph looks professional.
The present
What goes with it
Not needed on the day. Add one if you want the present to feel finished.
Filter
K&F Concept UV filter, 49mm
A clear disc of glass that screws onto the front of the lens and stays there. It costs little and it takes the scratch instead of the lens.
As an Amazon Associate I earn from qualifying purchases.
Two other ways to go
Another way
Sony FE 50mm f/1.4 GM
The same view as the small fifty, opened wider still. The background falls further away, and a room lit by lamps stops being a problem. It is heavier, it is dearer, and it is the lens they would never sell.
Another way
Sony FE 85mm f/1.8
Made for photographs of people. It is kind to faces and it lifts the person clean away from whatever is behind them.
As an Amazon Associate I earn from qualifying purchases.