This one is fairly obvious. The journal wasn't good enough to be indexed by Clarivate (the company that manages the Science Citation Index and calculates the impact factor) in 2021, hence the journal is hoping to be indexed in 2022 when Clarivate do next year's assessment.
For clarity, a lot of things are needed before one can get indexed by Clarivate. There are over 25 criteria. Some of them are not obvious, such as:
The authors must have affiliations, geographic diversity, and publication records that validate their participation in the scholarly community associated with the stated scope of the journal. The demographic of the contributing authors should be consistent with the topical and geographic characteristics of the Editorial Board.
Other criteria are practical:
Cited references, names, and affiliations must be published in Roman script to
allow rapid, accurate indexing, and easy comprehension by our global users.
And some can cause serious headaches for new publishers:
The journal must provide a readily accessible, clear statement of the commitment
to peer-review and/or editorial oversight of all published content. Primary
research articles must be subject to external peer review.
It's improbable APS will screw up the latter two of these examples because they've have done them before for other journals, but the first is not something that's within their direct control, and that could have caused the application to fail.