TikTok affecting quality of my edits...

I'm really confused here. I've started an Editing Account, and I've made some good Edits that are High Quality, Ultra HD, 4K, 60 fps. It looks great in my video editing software. (I'm on CapCut on my PC btw). But when I upload it to TikTok, it ruins the Quality. its goes from 4K to like 1080p. All the Sharpness, Clarity, Vignette Effects I added are gone. Just looks so blurry. I have the Upload High Definition Videos Setting on. Why is this happening? I've seen so many 8K 120 fps Videos on TikTok. And countless High Quality Ultra HD Edits and Videos. Why are my videos being ruined? There has to be a fix because I've seen so many High Quality Videos. Anyone know a fix? I'd really appreciate it.