We understand that you are experiencing an issue in that the Title you have specified in the plugin settings is not displaying as expected in the search results for your site. We checked on the page and did confirm that Yoast is outputting title as the following in the source code:
<title>Agence Web et Print Bourg en Bresse | ClicAInfo Bourg en Bresse</title>
However, we do see that this is not the title that Google is indexing in a search here. Whereas Google typically uses the title from the metadata for indexing, this is not always the case. Google will sometimes modify the title of the URL as it sees fit, as well as sometimes adding the brand or sitename to the end of your title. This is not due to the plugin not functioning as expected, but rather is due to Google modifying the Title it indexes as it’s algorithm has concluded that there is a better version to index.
We also have additional information on this topic available at the following links: https://yoast.com/google-page-title/ and https://kb.yoast.com/kb/google-shows-different-titles-for-my-site/. Please refer to these articles as the include recommendations for crafting a page title which will help increase the likelihood that Google will use the title you specified instead of modifying your page’s title as it sees fit.