Great news, this is now possible!
Liron Hilb Horev (PM, Duda) responded responded · May 28, 2023
I'm happy to update that we've implemented a feature that allows you to customize platform-generated assets like the default robots.txt and sitemap.xml files, and upload your own. This gives you more control over your website's SEO optimization and settings. To do this, go to the SEO & Settings tab in the editor. We hope you'll find this new option valuable and beneficial.
You will need support to help you. You have zero access to the root files so uploading files for adsense isn't possible unless you go the HTMl route with an HTML widget.
@shawnlutzko did you manage to resolve this? I'm having the same issue and dont want to have to move the site elsewhere.
This has been on the idea board for a while. I recommend that anyone who is interested vote up this feature request. https://ideas.duda.co/forums/930658-duda-idea-board/suggestions/41073523-upload-ads-txt-to-the-root-of-the-site
I managed to show ads in the places I wanted them to be. You simply paste the html code of the advertisement on different pages. However, I also keep getting the message that the TXT file has not yet been uploaded.