I don't use this feature, so I can't explain in detail (sorry), but I think it is a filter for previewing URLs pasted into posts.
If there are websites that contain harmful images or content in the OGP, you can use this feature to disable the preview of such sites.
Probably several people have published servers (for this feature), but the one I know of is @村上さん 's https://summaly.arkjp.net/.
Summaly itself is developed by @syuilo , and can be found here. https://github.com/syuilo/summaly
If anyone knows more about this, please add it.😇