That message is really strange. Obviously, you device is not incompatible with Windows 10 since you are running Windows 10 on your computer now.
You did mention that the computer is an antique, which means the Intel processor is old. I wonder if the RST software you installed is too recent a version, but you did say that Windows installed this version for you so that should not be the problem.
When I reinstalled RST after updating to RST, I let Intel chose the most appropriate version and it did not install the most recent one:

You can also see that iaStorAC.sys is the only installed driver, in contrast to your system, which has Optane and several other drivers listed. I'm not sure if the additional drivers are contributing to the problem.
Finally, note that the driver info in the figure above specifies the processor on my computer. The figure you posted the other day simply says "Intel Chipset" so I wonder if the RST version you installed is a generic one for older processors and works,
but Windows "sees" that you have an older chipset and thinks it is incompatible because Windows is unaware that Intel has provided an updated ACHI controller for older chipsets. I have no expertise in this area; I'm just trying to make some sense out of the
information we have.
Given that it is difficult for you to spend long stretches at the computer, perhaps your effort should be directed toward more productive work. Perhaps you should wait a month or so and then attempt the install againMaybe when Microsoft resolves the issue
that initiated this post, your configuration will be recognized as compatible and 1903 will install effortlessly. You clearly are able to work with your current version of Windows and 1903 is not so different, clearly not worth risking your comfort and health.
I certainly understand if it takes you days to respond, or you elect not to respond.