Why are my videos getting downgraded in quality?

I’m not new at this, have been doing it for years on the YouTube side, and on TikTok. But I have always seen a large downgrade in quality on TikTok.

Very strange considering it says 4K once I upload it but it’s very obviously half the quality or worse when I view it. Any way to fix or get around this?

It’s certainly not my media settings. I usually edit 4K high bitrate content that always exports at the same quality imported.