If you use Netlify (which I highly recommed, as the Quarto/GitHub/Netlify integration is so seamless), you can supply a redirects file that lists all the old urls and their new locations. Netlify builds from Quarto’s _site directory, so just put the _redirects file (here’s mine) in your _site folder, right? I tried that first, but it doesn’t work because the _site directory rebuilds when you rerender your site. Instead, I moved my file into the static folder, which gets copied over to _site as described above.
My use case here for redirects is pretty simple: I had a small number of urls to switch, and I don’t expect to frequently add to that list. If your situation is more complicated and/or you want that _redirects file to automatically generate shorter urls when you create new pages, there are options described here and here.