AOC CU34P2A
3440 x 1440 pixels, 34"
AOC CU34P2A
3440 x 1440 pixels, 34"
According to AOC's specifications, the monitor has a stand that allows height adjustability of up to 110 mm (11 cm). When the screen is set at its lowest point, this would mean that the distance from the base of the stand to the bottom of the screen is about 61 cm - 11 cm = 50 cm.
Issue can be due to several reasons. I imagine you have an outdated/old HDMI cable (version <1.3).
If you have a sufficiently newer version of HDMI cable (say HDMI 2.0), then perhaps its the dell usb-c adapter. Product description does not say thunderbolt, so it's only USB-C. Plus Apple is not among list of compatible brands. Is 1080p is the max you can get with all other slots unused on the dell
Ultra wide curved 34 inch screens cannot be rotated into pivot mode. This is a feature that is missing for those kind of displays. In case you did not order the product yet, you may also consider buying a 31.5 inch or 28 inch 4K display. 28 inch 4K displays with heigth adjustable stands can be rotated into pivot mode. The additional advantage of a 4K display, text is much sharper than on a 3440x1440