WP 5.4.1 and GT 2.7.6 when in a post and you inserted an image, under Settings – Block – Image settings:
you can set the image size but there used to be a Attachment Display Setting where you choose what to do when you click the image. That is not shown anymore.
Sometime I feel like I see it, then again later it is gone again.
PS: the changelog is not up to date.