How can I file an EB-3-based I-485 when I am on an EB-5-based conditional green card?

First, retain the services of an experienced EB-5 immigration attorney. If you obtain conditional permanent residency on the basis of an approved I-526 petition, you will then have to withdraw your conditional permanent residency in order for you to apply for permanent residency under an alternative EB category.

No, you have to surrender your current green card abroad and then apply for a new green card abroad based on the EB-3. You cannot switch from one green card to another. I-485 is only to switch from non-immigrant to immigrant.

You will need to be careful with your strategy. Essentially, you cannot hold two green cards at the same time. Before you apply for a new green card, you need to surrender your existing one. I assume that you will apply for a conditional green card following the approval of your I-526 petition. During your sustainment period while you are waiting to file form I-829, or after your sustainment period and filing of your I-829 when you are waiting for its approval, if your EB-3 becomes current and you wish then to file a new I-485, you will need to surrender your EB-5-based conditional green card first. Whether at that time this is a good strategy to implement or not depends on how far along the process you are with the EB-5. I am not sure who advised you that I-829 approval is taking four years now. The USCIS website today is giving a range of 27.5 to 47.5 months. As you can see, four years is the outside limit of that range. In summary, your strategy looks fine, but I strongly recommend that you do not execute it without the sound counsel of an immigration attorney who is current with the ever-changing rules and regulations and various processing times in EB-5 specifically and immigration generally.

It appears that there is a need to justify why this is necessary, as it is based on fear that one visa or the other may be denied or delayed (i.e., you are debating whether EB-3 will lead to faster permanent residency than EB-5). The answer to the debate depends on your nationality because there is no discernible fact that EB-3 is faster than EB-5, except perhaps for Chinese nationals who are experiencing severe retrogression. Furthermore, the general rule is if you have been approved for one residential status, the USCIS may not approve another one for you. In fact, you would have to give the first green card up before you can file the second (i.e., see all the rules governing filing Form I-407). Also, when it comes between EB-3 and EB-5, if you go for EB-3 rather than EB-5, I wonder what becomes of your exit strategies out of EB-5 where you had already invested $500,000. You may seek withdrawal but think about your subscription agreement and terms of exit with the regional center you are working with at that moment. Typically, your EB-5 investment would have been deployed the moment your I-526 has been approved, which is the general rule in EB-5 cases. So, what is the need to head to EB-3 at this point? Advisably, consult an EB-5 attorney and review your agreement to avoid unpleasant surprises and plot better strategies.

You cannot file an EB-3 adjustment unless the priority date is current. You cannot have two green cards, so if you get to the interview on the EB-3 first you will need to file an I-407 to abandon your two-year green card.

Once your EB-5-based I-485 is approved, you are a green card holder (i.e., a lawful permanent resident, albeit conditional). In order for you to backtrack and process for an EB-3 I-485/green card processing, you would have to withdraw your permanent residence, re-fee in and re-file for the I-485. That may be more time-consuming and require more effort than to file for the I-829.

Your question assumes a visa number is readily available under the EB-5 quota based on your country of birth; if so, while unusual you could arguably file your EB-3 based I-485 application for adjustment of status to see which is approved faster.

You cannot have a green card and file an I-485 without giving up the green card.

Good strategy.