https://www.theverge.com/2018/12/7/18126312/how-to-save-tumblr-porn-ban-export-tool-backup

On Monday, Tumblr announced that it’s removing all adult content from its site on December 17th. Any explicit sexual content and nudity that’s already on the site will be hidden and users won’t be able to post any more adult content.

That means reblogs and public posts will all be hidden. You’ll need some way of saving all your posts. Tumblr does offer an export tool, but it’s buried under multiple pages in the Help Center.