YouTube Shorts compression is absolutely nuking my 4K footage

I’m shooting on an A7IV and my exports out of Resolve look crisp on my desktop, but the second I upload to the Shorts shelf, it looks like it was filmed on a potato. I'm exporting at 4K (9:16) with a high bitrate, but the blockiness in the shadows is driving me nuts. I've tried downsampling to 1080p before uploading to see if the YT encoder would play nice, but it didn't help. Even tried messing with HEVC vs H.264 and it's the same result. Is there a specific bitrate "sweet spot" for the vertical player that I'm missing, or is YouTube just rolling the dice on which codec (VP9/AV1) you get for smaller channels? It’s frustrating seeing some creators with pin-sharp vertical video while mine looks like a 2010 webcam rip. Any tips or is this just "how it is" now?