[deleted],
I tried a variation on your suggestion. Here is what I have learned (for others who may be interested).
First, I installed the Nemo file manager (for Cinnamon) so I can open a file manager window as root.
Next I mounted my EFI partition at /boot in the Terminal app (so I can see the content of the /boot directory).
In Nemo, I navigated to the /boot directory, then opened a root instance of Nemo there. It now contains directories named EFI, loader, and System Volume Information as well as a file named solus-enroll-me.cer (I presume this is the signing key for MOK registration).
In the loader directory, I found a sub-directory named entries, and the loader.conf file you mentioned in your reply. I've been keeping notes on my investigations (I named it SolusNotes.txt), so I stored the content of loader.conf (just in case) there. It contains two lines of text, "timeout 5", and "default Solus-current-6.3.12-241.conf".
In my administrative instance of Nemo, I opened the loader.conf file (as root) in Kate, then changed the second line (as you suggested) to be "default @saved", and saved my change.
I closed all my opened windows and rebooted back into Solus to make sure that works. It does.
Next I rebooted to Windows to see if that works. It does (I can still boot to Windows O.K.)
Finally. I rebooted (one more time) to Solus, successfully.
The clr-boot-manager's boot menu now has the Windows entry selected (exactly as I want!, so I can reboot to the OS I am using following updates, etc. more easily).
One last question: Where can I find documentation/information on systemd-boot?
It's amazing how effective one small reply can be! I am genuinely grateful, and I can't thank you enough. Now I have my new Solus installation working exactly as I want it to. I am nor confident that I'll be a happy Solus user for many years to come (as well as - hopefully - a good community member)!
I know this reply has grown to be very long, but I hope it helps others who follow,
Ernie