It’s kinda goofy, but you have to use a special link or append the end of your URL with a bit of code. Once you do that, then when you download your games, they will download as .elf instead of .uf2.
Here’s a link you can use: https://arcade.makecode.com/?nolocalhost=1&compile=rawELF&hw=rpi#
It’ll take you to the dashboard and look like normal, but you’ll see that ‘compile=rawELF’ part in there that lets you know your downloads will come through as .elf files now.
Hope that helps!