It's an LG Dual Up (you can find the info in some earlier posts)
Technically it's 8:9 so not a perfect square, 2560 x 2880
https://www.lg.com/us/monitors/lg-28mq780-b-dualup-monitor
discontinued and going for almost double the msrp on ebay, alas
alt Hacker News
discontinued and going for almost double the msrp on ebay, alas