Problem of encoding characters (apostrophes) in my posts publications

This actually happens to me. I usually resolve this via string replace function.
First one replaces the WordPress Content area. The second filter is replacing the Title area.

Check out the str_replace array and insert your œ to your own string before the $content array.

function replace_the_content_filter( $content ) {

    if ( is_single() )
    // Add image to the beginning of each page
    $content = str_replace(array('«','"', '“', '”'), '"', $content);

    // Returns the content.
    return $content;
}
add_filter( 'the_content', 'replace_the_content_filter', 20 );

function replace_the_title_filter( $content ) {

    // Add image to the beginning of each page
    $content = str_replace(array('«','"', '“', '”'), '"', $content);

    // Returns the content.
    return $content;
}
add_filter( 'the_title', 'replace_the_title_filter', 20 );

I hope that helps. Please be careful on the Title or Content section. If you wanna do it on Attachment title then check the https://developer.wordpress.org/reference/hooks/wp_get_attachment_caption/.

Goodluck.