Quality on TikTok is set entirely at upload and cannot be improved afterwards by any tool. TikTok accepts up to 1080p, but only preserves it when the creator recorded at that resolution and had the high quality upload option enabled in their settings — an option that is off by default and that most people never find. The result is that a large share of TikTok, including plenty of videos with millions of views, exists only at 720p or below on TikTok's own servers.
This is why we show the resolutions that genuinely exist for the video you pasted rather than listing 1080p on every page. A tool that always offers 1080p is either upscaling, which increases file size without adding any detail, or simply mislabelling a 720p file. Neither gives you anything the source did not contain.
File size is the thing that has changed most. When TikTok was capped at sixty seconds, every download was a few megabytes and nobody thought about it. The limit is now ten minutes, and a long video at 1080p can pass 100 megabytes — enough to matter on a phone that is nearly full, or on a metered mobile connection. We show the real size next to every option for that reason.
One genuine advantage TikTok has over other platforms: audio is mixed into the video file. Reddit stores sound separately under DASH, and YouTube separates the streams above 720p, so both need a merge step that can go wrong and leave you with a silent file. TikTok does not. What you download plays with sound immediately, every time.