Interestingly, I’m not able to reproduce this at all, even if I force the X11 ozone backend on Chromium (this is with PipeWire from master and GNOME Shell 47.3).
The negotiated caps are: set format video/x-raw, format=(string)BGRx, width=(int)3840, height=(int)2160, framerate=(fraction)0/1, max-framerate=(fraction)60/1