Clicking Upload Button Brings Server Not Found Error

When I attempt to upload an image in the Appearance section (for example, the header), I get the server not found error message after clicking (submit, upload, whatever).

When I look at the URL address, I can see that the problem is that WordPress is sending the link but without the leading part of the address (https://www.cmtfp.org/…) It starts the URL with the blog directory. I’ve looked into the files to try and correct this without success.

This happened immediately after install. I’d hoped that the recent update corrected the problem, but it didn’t.

Help, please. ??