Permalinks causing all blog posts and new images to be 404

I’m transitioning my ten-year old WP blog from /blog to the main page. This morning I published my first post to the new blog and it came up 404. I turned off all my plugins and republished, still 404.

I was able to preview the post just fine, it’s only when it goes live that it is 404.

I set the permalinks to plain and that made the post show up, but then all the images in the post were broken. So I went to the Media area of the Dashboard. The images I’d uploaded to create the front page were/are still there, but all the ones I’d uploaded recently for the blog post were empty boxes. I tried uploading an image. The new image uploaded in that there was no error message and the box had a checkmark, indicated it was selected and could be added to a post. However, like the others, the thumbnail in Media showed only the empty box, no image.

When I inserted this empty-box image into the test post, it shows the proper metadata (the image name and alt tags) but no image.

Context: I’d had some trouble with the uploads folder previously, because when I copied over all the archival photos from the ten years of posts, they didn’t get integrated into the uploads folder. I used several plugins to pull the uploads in, but those plugins are off now. Just mentioning in case that could be a factor.

Also, I am using Yoast’s WordPress SEO, which did give me permalinks trouble several years ago.

However all plugins are off now.

So this is really two issues, but I think related to the same thing: how can I fix the permalinks such that I can have links based on post names and that my uploads folder works again? Thanks for any insight you can provide.