I decided to take a different approach - I'd install some other distros that support Xfce, to see whether any of those would support Bluetooth better than the Solus beta release does. To that end, on my spare laptop, I installed MX Linux and then Linux Mint, both of which I had used in the days before I discovered Solus, and both of which support Xfce.
I did full installs of both distros, not just trying the "Live" versions. MX Linux seemed to me t to be very primitive after using Solus for so many years. I tried to enable my Bluetooth mouse and was unable to. It did not appear to me that it was using the same software that Solus does. Without a functioning mouse, I abandoned that experiment.
Afterward, I installed Linux Mint. This time it was apparent that it used the same Blueman Bluetooth manager that Solus does. And my results were exactly the same as with Solus. I was able to pair and connect my Bluetooth mouse, and use it successfully. However, although I could pair, connect, and trust my Bluetooth keyboard, I was unable to type a single character in the terminal with it.
I've devoted a lot of time to this project, and can only conclude that at present, it's not well suited to folks who would want to use it the same way I would. That's probably a very small part of the potential user pool, so the problem I've experienced may never affect any of Solus' Xfce users. And I'm fine with that.
Since KDE Plasma is my DE of choice, I'm going to abandon Xfce for now, and maybe give it another try when it's no longer a beta. I remain very impressed with Xfce - apart from the problem I've described. It just wouldn't work for me as-is.