1. file the paperwork to have it be a legal SBR
2. remove the device (and no, you can't just remove the device and keep it at home either, it must be made permanently inoperable or get rid of it) and ATF will waive the $200 tax. No word on how long it will take for the ATF to approve the SBR. Some experts in the field say it could backlog the approval system for restricted weapons from the current months to years)
3. turn it into a legal size rifle
4. turn the entire pistol with a "device" into the ATF for destruction.
If you don't comply you could potentially get up to 10 yrs in prison.
b.t.w. what was announced was NOT the proposed rule in 2022, with the form 4999 and the "point system" for determining if the pistol with a brace is an SBR or not, that's gone. In it's place is something far worse. ATF will basically look at your pistol with the "device" attached and determine if it passes or fails, based on some subjective vague statements. Instead of the old "If the length of pull is over 12.5 inches then X points" it's now something to the effect of if the length of pull is "similar to a rifle", and ATF will determine this, not the gun owner. This new ruling (which they did not take comments on like the earlier proposed rule) is hundreds of pages long. If this is allowed to stand legally there will be nothing to stop the ATF and the Biden administration AG to restrict some pistols without a stabilizing brace also, like for example a new rule saying any pistols that have a "similar" weight or length to a rifle are rifles also. The words "similar to" are used a lot in this new ruling.
To me the subjectiveness and ambiguity of it is like driving down the road and having a Sheriff pull me over for speeding, with the Sheriff saying there is a speed limit but he won't tell me what it is exactly, and basically he gets to look at me driving down the road and to decide if I'm speeding or not.

https://www.atf.gov/rules-and-regulatio ... ing-braces
There is currently a lawsuit , SAF vs. ATF, and the judge might issue a stay on this ruling until it can work it's way through the courts. In addition a lot of other gun groups, NRA-ILA, GOA, etc. might also sue. Plus there is this:
https://www.breitbart.com/2nd-amendment ... race-rule/