If you want to see what the 60 megapixel sensor of the Sony A7R IV can deliver, this is a reference example that maybe cannot be beaten.
This series from f/2 through f/8 evaluates the Voigtlander 65mm f/2 Macro APO-Lanthar on an extremely demanding subject that makes mincemeat of most lenses, mercilessly revealing every weakness, lack of symmetry, etc. Most lenses require f/5.6 or f/8 to sharpen the whole mosaic.
Includes images up to full camera resolution of 60 megapixels.
The about $999 Voigtlander 65mm f/2 Macro APO-Lanthar surely is a must-have lens and a 'steal' for any Sony shooter for whom manual focus is acceptable. Meaning go buy one right now if you are serious about image quality on the Sony A7R IV.
This is the best lens so far that I have tested on the Sony A7R IV— few lenses approach it, let alone deliver what it does at f/4.