Just in case someone visits this thread at some point, and I know of at least one other thread regarding this same issue, I wanted to close it out with a final denouement post. Apple's Mac OS Catalina update 10.15.6 seems to have solved the issue. System Report now shows the RAM in my still very much new (and even more loved now that I've had more than a month's worth of intense WFH time to get to know it better), MacBook Air 2020 as being:
16 GB 3733 MHz LPDDR4X
The "X" in the LPDDR4X was hiding in plain sight all along. Apparently the OS update was all that was needed to bring it out into the open. It would seem that System Report can report flawed information on occasion. I did not think that was a possibility, nor did Support when I discussed the problem with them. On the Monday of a week in which the MLB finally starts back up, I am happy to report there is, in fact, joy in Mudville.
Stay safe everyone.
-- JDee
PS For anyone wondering, I updated my MBA via System Preferences --> Software Update. That method, however, did not work so well on my fairly ancient (mid-2012) iMac. I think the update was interrupted somehow overnight and right after, I encountered all kinds of restart issues. I ending up using the combo update download as part of a successful restart troubleshooting effort. Big, big shout out to Kappy's excellent post entitled: "A Troubleshooting Procedure that may Fix Problems with macOS El Capitan or Later," which guided the effort and recommended the use of the combo updater.