Here is another link corroborating yours (albeit shorter)
The takeaway here is it's a trap the ATF has set: turn in your paperwork describing your now illegally owned gun and if at the end of 88 days they haven't processed it to give you your permission slip... ooops you get a felony. How convenient on their part!
Info from a ATF / NICS online training session. FEB 1, 2023
The 88 days is a FBI Background check only. If denied that means there is a background problem (felony, domestic violence, mentally incompetent or so forth).
If the SBR Form 1 is denied due to problems (clerical) it can still be resbmitted, as long as it was started in the initial 120 days.
If totally Denied you still have the option to:
1. Remove the brace, and configure to pistol buffer tube only . Preferably destroying the brace or removing from the area of the pistol.
2. Add a 16" or longer barrel
3 Destroy the Firearm
4. Turn in the the ATF.
We have removed all pistols with attached stabilizing braces that were listed on GunBroker.com in the Pistol Category, these were legal prior to rule 2021-08R. We will continue to monitor and remove all listings or relisting that do not comply.
To relist those items, one of the following criteria must be met:
THIS IS FROM GUNBROKER SUPPORT. 😐️
It will get to the point you will have to have a supervisor if you fire your gun... just give it time... It's coming..