mattleein regards to px:
"Image area size" of callout > image used to have px as an option as per the wayback machine instead of %
https://web.archive.org/web/20250407152703/https://learn.microsoft.com/en-us/power-bi/visuals/power-bi-visualization-card-visual-new-format-settings
"Image area size
Define the image area size between 10% and 90% with this feature. When the Fix size toggle is enabled, this area size option changes to to a Size option where you can input the number of pixels instead"
If you want 2 visuals of different widths, both with a fixed size svg on the left and content on the right, being forced to choose image area as %
means the image area is a different size based on the width of the visual. Should be able to specify a fixed px image area