I don't think that functionality exists for Backdrop's Feeds. Best way to find out is to post a question in the Feeds Github issue queue, so that the maintainers can respond.
Just to clarify it appears that the item: Fix Search for "On the Web" module, is about the search on backdropcms.org at https://backdropcms.org/modules
Comments
I've never imported comments with Feeds in D7. How do you do that?
Never done it in Drupal7 either, but from D7 to D9
I don't think that functionality exists for Backdrop's Feeds. Best way to find out is to post a question in the Feeds Github issue queue, so that the maintainers can respond.
https://github.com/backdrop-contrib/feeds/issues
An upgrade from D7 to Backdrop will include the comments by default, unless you have opted to do a migration manually instead.
If so, have you tried Migrate?