It looks like the issue with SD cards is due to an SDK change made by Google in the name of security. They state that using the Media Store API is much faster than the file path access. Every developer started getting slow SD Card performance using file path access starting with Android 11. Android 12 will not improve the situation. Apparently, all file path access is being diverted through a very slow Java security module designed to be quickly modifiable by Google in order to combat security threats. End result: depending on the exact access pattern of the software, developers are seeing between 1/2 and 1/10th of performance they saw under Android 10.
Downloads to an SD card will be slow unless the code is modified to use the Media Store API.
Creating an internal write cache in order to Increase the size of chucks saved to the SD Card by 16x might improve performance a little by reducing the number of calls to the slow API.
