The feeds works on the demo, but not on my site

Hi Szaby, I can run a feed on your demo site, but not on my blog. I created an access for you on kisded@yahoo.com, please check your spam. There is a password to view the site : Login : entrer Pass : dedans. What I do : I take a URL, for example this one : https://www.boursorama.com/patrimoine/immobilier/. The I pass it in this service : https://rss.app/, it gives me this feed URL : https://rss.app/feeds/gbwiMuN8sCSwHouD.xml. If I use it in the demo theme it works, but if I use it in my theme it doesn't work, although I apply exactly the same settings. Can you help ? Thanks.