Thanks for the link. Now that I understand better this part of the Developer Options, I found more information. However there is one thing I am not sure of...
About 1/2 of my apps are greyed out with a standby status of either "Never" or "Exempted". I think the "Exempted" ones may all be apps where, in the normal app settings, I set the specific app to have "Unrestricted" battery access. But the ones that have a status of "Never", "Rare", or "Restricted" all are set in the app to have optimized battery use, (probably set to that on installation). So the system must be choosing the standby status of apps that have battery use set to optimized?
By the way, my Gmail standby status is set to "Exempted". But I now use FairEmail so the Gmail app is unused.