Hi and welcome! Hopefully one of our plumbing experts will be by soon, but it might be helpful if you can post a “zoomed out” pic showing more of your plumbing. That might help to identify what this additional pipe could be for.
I have a similar pipe and when I asked my builder what it is for they told me it goes to where the skimmer overflow line discharges water in the ground in case excess water needs to be sucked out.
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