This is actually something that is controlled by your theme. Take a look within your theme files and find a “tribe-events >single.php” file. There you should see reference to the image being pulled there and can choose a different size (any of the default or a new one registered with add_image_size()) or remove that section completely.
Actually, that is too much.
When deleting what you said, my picture also went…
So in the end I found it, (I think) and I just deleted line 43 in my screenshot and that got rid of the blue section, while keeping my picture in the post as intended, but without the blue overlay.
😉