when using the Navigation as Header; the logo gets its size from the Menu Item height ( set in Customizer > Layout > Primary Navigation ). You can either:
1. Reduce the menu item height
OR
2. Use some CSS to make just the logo smaller:
Hello, thank you for your answer. The problem is that by adding the css code, I cannot for example increase the height of the menu item without making the logo larger …
Oh sorry that looks good to me. In the preview in the customizer I saw the logo very large. On the other hand when I go on mobile the problem seems to be solved.