Just to let you know what has transpired.
I contacted NB yesterday (thanks for the link, Tony) and they responded within a few hours with a file to download and install. I installed it and all seems to be fine: no watermark.
I noticed a file (created May 12) in my download folder yesterday entitled, "NewBlueVideoEssentialsForWindowsSetup30-140723.exe".
I don't recall downloading this or installing it.
The new file that NB sent yesterday has almost exactly the same name. This suggests to me that somehow an automatic update got installed, but it was the wrong one. NB didn't suggest any involvement, but nor did they seem at all surprised when I described the problem...they just sent the fix.
All's well that ends well, and I was very impressed with the speed and efficacy of NB's customer service.
Regards,
Dan
Power Director 21-Ultimate
v 21.0.3111.0
XPS-8940, Win-10 64-bit,
Intel Core i9-10900 processor
(10 core, 20M Cache),
32GB DDR4 RAM, 2TB M.2 PCIe NVME SSD, 2TB 7200 RPM SATA HDD,
NVIDIA GeForce RTX 2060 SUPER 8GB GDDR6