I also want to chime in that this seems like a feature that should be included in the default shopify install.
Especially since you can sort by Modified in the Products Admin.
Just checking in on these newer posts to say I've also submitted feature requests on this topic for each of you here. Our team can review these requests, so hopefully, this can be something that is available in the future.
There is never a guarantee that a request will get a Green Light, *or* make it to a product launch, but we really do appreciate you reaching out with your suggestions. As our development team are working on releasing newer features as well as updating older features of the platform, I would not be able to give a timeline for when this (or if) this will be available.
In the meantime, the app @kpvw mentioned in the first page of this post, Advanced Collections, should let you sort by last modified in your collections. I know using an app is not the best workaround, but it is the best option for now!
Hope this helps!
Social Care | help.shopify.com
@Ava, it's been 1.5 years since you added this feature request. What's the current status?
Sorting by publishing date is very important to us so that we can display seasonal products like strawberries (same product as last year, but 'new' in season) at the beginning of the collection, not the end.