Thank you wackyblackie. Actually, I withdraw my previous self-answer that the .htaccess file with the redirect has has to be in the htdocs folder. It is actually impossible to tell which change made the difference because of the long delay in the server’s reaction to changes due to the strong server-side caching.
This has actually become an additional problem for me, because the redirection was only an experiment and was never intended to be permanent, so once I established that the .htaccess redirect works, I removed it from the .htaccess file. However, it is still redirecting many hours after removing the redirect. And I can prove it’s not due to local caching in my browser, because, in addition to clearing my browser cache, I also tried accessing the page in a different, newly-installed browser in which I have never visited that site, and even there the redirection is occurring as if the redirect is still present in the updated .htaccess file.
I have tried disabling caching by following the advice of anon19508339 in this thread, but it hasn’t yet had the desired effect. I have seen other complaints on this forum about the server-side caching preventing website owners’ changes from taking effect within a reasonable time, and I hope there is a solution to that that works.