3440 × 1440 vs 3840 × 2160
UltraWide QHD against 4K UHD, side by side.
3840×2160 renders 3,340,800 more pixels than 3440×1440 — 67% more. They differ in shape too: 3440×1440 is 21:9 while 3840×2160 is 16:9, so windows and video fit differently. At 4K UHD's pixel count you'll typically run OS display scaling above 100% for readable text.