How can I file a another I-485 as a dependent through my spouse while my I-485 application as a primary is still pending?

You can try and file a second adjustment application although USCIS now prefers that you transfer the underlying basis for the existing petition as explained on their website.

You have an involved situation. You need a consultation appointment with an immigration attorney.

If you are in valid nonimmigrant status in the US, your spouse can file I-130 and link it to your pending I-485.

You could apply through your spouse. However, there are several matters to consider. How did your spouse obtain the green card? If it was employment-based, did she have you as a dependent beneficiary? Assuming she did not have you as a dependent/beneficiary, and since your spouse is only a green card holder, then you cannot apply right away for the I-485. Your spouse would need to petition for your first (via I-130) and once this case is approved, then you can apply for the I-485. We hope this helps.

A person can have more than one I-485 pending but discuss with your attorney regarding your eligibility to file.

If you are in valid, nonimmigrant status yes, your spouse can file an I-130 and you can link it to your existing I-485. If not, no, she can file the I-130 but you cannot adjust based on it.

You may have both cases pending simultaneously.