The rule has not been published on the Federal Register yet. An ATF spokesman said that it will be published on January 31, 2023. After that, look for litigation to start being filed. This search should find it when it's published:
Search Federal Register
The pre-announcement on January 13th has caused lots of heat (emotion) and much less light (rational reaction).
There have already been some mis-steps by the agency, including the error in their FAQs (well, they say it's an error, but it must be corrected) about sharing registered items in your personal presence being prohibited. That generated more heat.
Most of the 10 to 40 million owners of these firearms have never filed NFA paperwork, and don't want to. The ATF estimate of 3 million of these firearms is likely considerably under the reality, meaning that the agency will probably be overwhelmed. The online system can be a bit confusing if you have never done it, and you have to get every detail right - so take your time and read everything as you go. Remember that you need to get fingerprint cards done on the right forms or correct electronic files. UPS shops and many gun shops have the right equipment.
The reality of all this is that we're likely to see a number of interesting things in the next few months. Some of them bureaucratic and procedural based on an overworked overwhelmed agency trying to deal with political pressure from the top. Some of them legal and based on potential violation of Constitutionally guaranteed rights of citizens. Some of them groundbreaking and based on mistakes made in the past by Congress and their deep state agencies. But in all this, law respecting gun owners will be caught in the middle, and a Federal agency that is chartered with helping stop criminals from misusing firearms will be distracted by the questionable direction of their political leadership.
The Chinese curse is said to be, "may you live in interesting times..."