Hello, I am the original poster on this topic. I ended up selling the tablet at a loss (I had a 14 day return window for the tablet, but while I was trying things, it passed).
First, let me say that Samsung S6 Lite tablet, which is considerably more expensive, has the same problem. So it is clear to me that this is a "hidden" business practice to force customers to buy their S series (again, the S Lite variant does NOT work).
During my reluctant research, I found that the main technical reason is that both the A series and the S Lite series have a USB 2.0 protocol for the USB-C port. I actually knew even before buying my A tablet, that it is USB 2.0, but I could not possibly guess that simultaneous OTG and charging will not work.
I found a possible solution with the following adapter, but it costs $39.99 and it is not guaranteed to work with the A 2020 tablet because it is not in the compatibility list -- see https://lavaaccessory.com/samsung-tablet-adapters-support/tl-002-compatibility-list/ . In fact, I see there is variable success with different tablets and even different sub-models of the same tablet model. All this indicates that Samsung has not provided official and standard information to third-party companies who wish or may wish to fill the need.
And, to be honest, once I saw that there are possible incompatibilities, I started worrying about possible electric malfunctions / fire hazards due to using a non-Samsung adapter. Why not? If something bad happens, even if it is relatively benign (not to mention if an explosion happens), I guess Samsung will just say they are not responsible for anything when using an unofficial adapter with extra complexity like the aforementioned SIMULCHARGE adapter.
Now, I should say that the problem is not with Samsung only, all manufacturers are like this with their analogous models (USB 2.0 with USB-C). Someone please correct me if he knows of a counterexample.
Some more info: notice how it is mentioned on the main page of the SIMULCHARGE adapter that "Works with out-of-the-box (unrooted) tablets". Notice the word "unrooted". "Rooting" a tablet of course would automatically void the warranty, and anyway, I think rooting these days is extremely undesirable. For example, https://forum.xda-developers.com/t/android-tab-which-supports-otg-and-charging-at-the-same-time.3896... mentions "if you're rooted you may be able to control the charge controller directly" and the same post adds additional advice. Later on the thread, someone else reported making it work with a Y-type USB cable with an older version of the A tablet.
There is a similar discussion here: https://android.stackexchange.com/questions/157856/simultaneous-usb-otg-and-charging
Notice how even if you have or build the right Y-type cable, rooting and even subsequent Android kernel changes may be needed.
So, no official solutions, any other requires considerable time and/or expense and again, I am seriously concerned about the electrical / fire safety of these unofficial solutions/methods, especially when a tablet with a battery is involved, not to mention the void warranty if rooting is really needed.
If a Samsung representative reads this, they should understand that they are seriously misleading their customers by not providing accurate information about charging not officially supported with USB devices. This is seriously misleading and such a waste of time and energy, that I will really not buy another Samsung product for the foreseeable future, if at all.
Now, someone will say that an iPad (a normal non USB-C iPad) is considerably more expensive. But it is actually not, considering that USB devices and charging works for sure with an official adapter, and that you get around 6 years of guaranteed software updates, whereas the Samsung A series will probably be without updates in 2 years.
