1080p suits almost everyone. It looks sharp on phones and laptops and keeps file sizes sensible for limited storage or mobile data.
720p is the practical choice when saving data or filling a phone with lots of videos — still clear on a small screen at roughly half the size.
1440p and 4K are worth it only when the uploader actually published at that resolution and you'll watch on a large screen. These files are big and take noticeably longer to prepare.
The list you see is generated live from the video itself, so you're never offered a quality that doesn't exist. If 4K isn't listed, the original simply wasn't uploaded in 4K. We never upscale, because upscaling adds file size without adding real detail.