Here is an update on this issue.
First, thanks to those who replied. But it seems that Apple Music was/is not the issue.
Apple Music was not the source of my problem as suggested by Fiend and Lou_Lou_Lou as it appeared BEFORE I signed up for, or installed, Apple Music.
Similarly, Apple Music was not the solution as suggested by Samuel-F as it did not fix the problem after I did subscribe to it.
I was able to resolve the issue after contacting Apple Support (not nearly as difficult as I thought it would be). Thank-you to 2nd tier support tech Michael. For some reason when I opened iTunes after updating iTunes to 12.13.10.3 (on my Windows 11 PC) it decided to rewrite my .../Music/iTunes/iTunes Library.itl file using only the content that I had purchased from the iTunes Store. Why it did this is not clear, but I believe it may have to do with the update adding "support" for Apple Music. Fortunately, it created a new one but left an old .itl file in my iTunes folder.
Michael walked me through a procedure to re-build my iTunes Library from the old .itl file. I had to close iTunes and then start it again while holding down the <Shift> key. I then selected the old .itl file when prompted during startup. That allowed me to see my entire previous music library in my .../Music/iTunes/iTunes Media folder, as well as playlists and podcasts too. After that, Apple Music/iTunes Match did its thing as advertised and uploaded my music from CDs and playlists to iCloud. So now I can see ALL my music and playlists both on my PC with iTunes and on my iPhone with Apple Music. {Happy Dance!}
A couple of comments on this "launch iTunes while holding down <shift>" procedure. I have a vague memory of having to do this to fix an iTunes problem in the past. So it is not something new. I did a couple of Google searches looking for documentation on it. I didn't spend a lot of time, but I only found one reference to it on an Apple Community post talking about the equivalent procedure on a Mac. So it doesn't seem to be well documented.
Again, thanks to all who responded. I hope this information can help someone else.