This new law only applies to firearms dealers. It does not apply to individual gun owners selling their personal collections.
The rule is 500 pages long, and there’s some question about what constitutes a “firearms dealer.” Depending on how you interpret the rule, it could mean anyone selling a firearm for profit. Dettlebach has been asked repeatedly how many such firearms would make a seller a dealer, and he’s dodged the question every time with the answer, “it depends…”
I wouldn’t trust the ATF in this regard. Or any other regard, for that matter.