X88,   Well as you see here, the R820 shows support to 21.3.4-0001, which would be the latest for that platform.  From the update you linked, the only thing it lists to resolve is the battery being marked low issue. So I don't see it showing that it would address anything differently betwen those two update versions at the disk level.     
Hello, Looking at Dell PERC H710P Adapter firmware release 21.3.5-0002 / Compatibility systems: R820 is not in the list. [URL] Why? Please advise.      
H710P firmware compatibility ... R820