How would Google differentiate between these two?

An expired domain with good backlink profile and a newly registered domain with mass built links before indexing the site?

In both cases the whois registration date is the same day as the day the domain was re-registered (in case of expired domain)/ registered (in case of new domain).

Or are there any factors at play here?

Bump.

An expired domain with good backlink profile will have old links. From previous years.

New registered domains will have new links from year 2023

ita said:

An expired domain with good backlink profile will have old links. From previous years.

New registered domains will have new links from year 2023

Click to expand...

What if the links on new site are only niche edits of old articles?

The date links were built. Or am I missing something?

Also you should not forget, that an expired domain was cached at some point. Despite this is uncertain, logic suggests that being previously cached could mean that Google already had track of such domain therefore could be recognized as something with previous activity. The importance of this could be low, but adding this up that the fact that the domains linking as some others have pointed out, were also longer aged, this could generate a significate differentiation.

Moreover, regardless of this aging factors, you are saying that the not registered domain, was blasted/mass built links before register. Mass built links generally never create a good reputation, so by that time when Mr. G passes one of those amazing "spam scans", the site could be dropping. Google works interatively, its constantly passing "tests" to the sites. This is why it's so surprising to many people: once their site stay happy and alive for 1 year straight, then it drops brutally, and the guy it's completely confused because it did not happen before, until it happens.