Ok, I'm going to be pedantic because I work in niche tech and just can't not (and this is wandering OT for this thread...which is saying something ) the CAT5 standard has been deprecated in favor of CAT5E since 2001 (!). None of my last several laptops have had onboard Ethernet* (a casualty of me wanting a slim and light notebook for portability -- there are semiportable tanks with Ethernet still on board but the idea of dragging one of those through all of the sights in this thread and then some is not appealing). Working in a corner of the industry where wired Ethernet is very much a critical connection method, the tradeoff is that I have a handful of USB-C Gigabit ethernet dongles in my bag for various reasons.

That pedantry aside, note the placard above the jack is labeled "MODEM CONNECTION" -- I doubt that it, if there is anything on the other end, it is most certainly not any form of Ethernet and rather an analog telephone line for modems (ahh,.. remember the dulcet tones of beeeep...screeeeeeeeeeech..tone...screeeceechhhhhh hhh....) and I can't remember the last time I had a laptop with a modem, let alone using said modem. And if you want to talk about less reliable and lower speed connections, boy do I have a candidate for you -- I'm sure someone probably has a USB modem for some niche reason but the venn diagram overlap of said people with niche reason and UA club members has to be awfully small...

(FWIW, UA has been through at least two phone systems in EWR since that placard would seem to have been installed so if it still had anything on the other end it was because someone went to a conscious effort to make it go somewhere. I have a feeling like the wall mounted phone that once adorned the other side of the outlet no one has had the motivation to make it not be there)