Featured image in Twenty twenty theme

Sorry about that.

For the Twenty-Twenty-Theme, I think a so-called “Child Theme” would be very suitable to realize your suggestions. You can find more about this on the WordPress Developer page.

That can then look something like this for the “Read more” text:

function twenty_twenty_add_read_more( $more ) {
    return '... <a href="' . get_permalink( get_the_ID() ) . '"> Read more <span class="screen-reader-text">“' . get_the_title( get_the_ID() ) . '”</span></a>';
}
add_filter('excerpt_more', 'twenty_twenty_add_read_more' );

And for hiding the featured image in a post you can possibly use:

if ( is_single() && 'post' == get_post_type() ) {
    //There is most likely a post being displayed right now.
}

I put the whole Child Theme, implemented with your suggestions, into one GitHub project. The link to it is here. You can just go to Code > Download and download it. It should work – I guess.

Have a nice day, Chris