gallery shortcode size parameter without effect

Hey there,

does anybody of you know, why the gallery shortcode always displays images in the same size, even if you add the size attribute and set it to medium, large or full?
Is this a bug?
The html looks like this:
<!– wp:shortcode –> [gallery size=\"full\" ids=\"$img1\"] <!– /wp:shortcode –>
$img1 is a numeric id of an existing image

The blogpost uses Gutenberg Blocks. Somehow the different sizes do not seem to have any effect.
Is there a different shortcode for placing images in gutenberg?

Greetings!