Imgur now blocks several VPNs and have issues loading embedded previews in several fediverse platforms. So instead of using imgur, you could use one of the following alternatives for uploading your images.
https://postimages.org/
https://imgbox.com/
https://imgbb.com/
https://www.imagebam.com/
@aleph As an instance admin myself, we are looking into fine-tuning those settings to limit uploads of an x amount in file size. But are we are looking into some thumbnail library to reduce the image sizes indeed.