Well, thanks for the info. I wish I had had that info before I had purchased this iPad. Well, the idea was to purchase an older iPad specifically to use as a HomePod with a screen. But, as you astutely pointed out, my Home App CANNOT see my HomePod mini. My iOS version is 10.3.3. So, bad purchase, bad decision.
This particular iPad is very limited in its usefulness as a HomePod. I can set it to be listening for "Hey, Siri" even from the lockscreen, but it usually does not hear me well and I have to say it several times and be pretty close to it. Then, depending on the command, it makes me unlock it before it does as asked. E.g., "Close my garage door" will not work unless I unlock it first. Bummer!
I will say that Siri seems much more limited in its functioning than Alexa, but then I do not wish to give up all my privacy for the convenience. I had to create a Homebridge out of an old Mac just to be able to use the Home app or Siri to connect with MyQ, Ring, TP-Llink Kasa, & Wyze. The number of things that are native or "certified" to work with Homekit are pitiful.