How to I get my Sharepoint Designer re-install to work?

My Windows 10 SSD was corrupted and I replaced it with a Windows 11 SSD. For over 20 years, I used Sharepoint Designer to successfully design four HTML websites, and enjoyed the application. I must have installed it using a CD-ROM, because I could not find the installer EXE file after I restored my documents and settings. So, I dowloaded and installed Sharepoint Designer 2013, but am unable to make it work. The User Interface is completely different from what my previous version of the application looked like a month ago. It shows two websites on the upper left of the screen, basically one with and one without WWW. I tried various ways to re-open my website, and kept getting this error message: "Microsoft Sharepoint Designer does not support editing non-Sharepoint sites." Before, I had set .html files to always open in Sharepoint and double-clicked them. So, I set Sharepoint as the default application for .html files as before, but when I double-clicked the one I need to edit, I got this error message: "You must first open a Web site before editing external webpages." When I click the Open Site button, I see a three versions of the website, one with the URL followed by : "/%2f"; when I select this one, sometimes it asks me for the ID and PW I use to access my site with my webhost, so something is going on, but I still get the "Microsoft Sharepoint Designer does not support editing non-Sharepoint sites." I deleted a lot of files in "C:\Users\henry\AppData\Local\Microsoft\WebsiteCache" subfolders, but that didn't work. How the heck can I get Sharepoint Designer to work again? I have depended on it for over 20 years! Totally stumped here!