Is it in the app, or in the platform? In the platform you can filter out NSFW content, then also in the app you can filter out or blur content. Not sure which you’re referring to, so hard to comment. Ideally try an both platform & app. If this isn’t working, then it would seem to be a tagging issue.

They seem to blur if the image is in a lemmy instance, but if it previews a link from a third party image host I have found it hit and miss.