1080 × 2400 vs 1440 × 3120
FHD+ (phone) against QHD+ (phone), side by side.
1440×3120 renders 1,900,800 more pixels than 1080×2400 — 73% more. They differ in shape too: 1080×2400 is 9:20 while 1440×3120 is 9:19.5, so windows and video fit differently.
Subtler than the spec sheet suggests: many QHD+ flagships ship rendering at FHD+ by default, and at arm's length most eyes struggle to tell 400 from 500 PPI. QHD+ matters for VR-style close viewing and bragging rights; FHD+ wins battery life. Try the toggle before assuming you need the pixels.