Your URL encoding is off, characters like é usually have to be encoded as well.
I created a vault named: Mon Réseau de Savoir
The below was able to open it, on IOS.
obsidian://open?vault=Mon%20R%C3%A9seau%20de%20Savoir
I used the below link to convert the vault name I used to URL Encoded: (Input box under section titled “ URL Encoding Functions”)