Fedora 38 Silverblue, final
Well, a complete disaster didn't happen, but I still had no luck wtih Silverblue. When I took the next step with the installer, I wasn't offered a choice of partition to install into. The installer just started up and I resigned myself to overwriting Solus Plasma on this machine, since it appeared that it was already destroyed. So I set about configuring that hardware-installed version of Silverblue.
Long story short: Things went okay for a while, and it was nice to use Silverblue at full-screen and on hardware instead of software. But after much effort, it was still a failure in my opinion. This time, the Software application was present in the dock at the bottom, so I was able to update the system, and I tried to use that to install the software I needed or wanted, but that was not gonna happen.
Using the Software app, there was no apparent way to enter the name of a package I wanted to install. I had to pick the packages from a list of app icons that was several thousand long, and not entirely alphabetical. To be sure I didn't miss what I was looking for, I had to check each icon as I scrolled through them, and after about 5 minutes of that, I decided "fsck this," and went back to the terminal to try my luck with flatpack again.
Turns out, there was no difference at all between the hardware version and the VM. (I've never seen any, really.) I got exactly the same error after confirming that everything I wanted to install was available. Cancelled by peer, whatever that really means.
So once again I was able to install and setup Silverblue (mostly), but not able to live with the results. Still no menu was apparent anywhere, and I could find no way to install the software I needed or wanted. I was even willing to work with Firefox, since Vivaldi isn't available via flatpak, but even by making that concession it was useless for me to keep trying. I gave up, inserted my Solus 4.3 Plasma USB drive, and rebooted, intending to nuke the entire SSD using the KDE Partition Manager from the "Live" session, and change to my other laptop to continue this story.
Then a miricle happened. I was able to reboot my original Solus Plasma partition! Although it wasn't apparent to me, the Silverblue installer did put that OS in the SSD's unallocated space, without actially being told to do that. So I'm back on the original laptop, in the original Plasma, with all my original configuration, AND I still have Silverblue available as well. Not a bad failure, as these things go. I may even boot Silverblue again sometime, if I can determine that there really is some way to go forward with it.

Well, maybe not. When I checked the SSD, I got a message saying that no btrfs support is present, so for now, there would be no way to boot that OS. Still, I'll probably just nuke that back to unallocated space and use it for the next interesting distro that I feel compelled to install on hardware.
So, this is really, really the end of my Fedora 38 Silverblue adventure. I wish it could have ended differently. Whoever made this distro "popular" must have had much different expectations that I do.