Thanks to everyone for their helpful comments and advice. I have now, at last, restored my Macbook to the older macOS (High Sierra, which I wanted), though the Macbook had to be totally erased and the downgrade took a few hours.
I made the mistake of upgrading to Catalina. Make that huge mistake. Not only does it mess with the HD on my MacBook Pro, but it messed with every Pages file in my system and change the file structure to Apple's latest file structure to suit SSDs which I have been using for a decade now. I publish a daily web site (mybirdie.ca) for the past 12.5 years now and have files stored for usage in future that number in the hundreds. My backup Mac Mini is on High Sierra and nearly everything I try to use, will not function with Catalina files and vice versa. Catalina also killed so many of the apps I use daily, citing it could not run them, that it left me in big trouble.
Thank goodness I not only use Time Machine but also do a daily clone via Carbon Copy Cloner. I reverted to Mohave by erasing the HD using Disk Utility and replacing the OS, then ridding myself of Catalina, never to upgrade again as the new file structure creates so many issues I simply refuse to deal with it.
Beware Catalina, if you have more than one Mac you use as a backup system. I suspect I will be on Mohave for the next decade.
Apple, always tinkering with stuff that worked fine until they touched it. Never again.