Thank you, Leo, for your astonishingly fast reply.
I will have to learn GenerateBlocks and that GutenStuff…later. No time now to invest in the learning curves involved. (I still use the Classic Editor plugin even.)
Meanwhile, I guess I’ll stick with what I already know how to do and create a special one-use page template as a stop-gap measure.
My plan is to share the result of my work here. Then I plan to mark this as resolved. Is it OK to do it that way?