H1B transfer will not impact your I-485 processing. However if your employer withdraw the I-140 before it is approved or the downgrade is denied for whatever reason, the I-485 will get denied.
You should wait for the I-140 approval and also get the EAD/AP before switching the job.
Your new job should be in same or similar position and your new employer should be willing to file I-485J suppliment to prove that the green card job offer exists for you and they will be able to pay you the salary mentioned in the PERM.
If possible, just stick with your current employer as your PD in EB3 can get current by end of this year or early next year and your green card may get approved by mid of next year.
@Kalpesh_Dalwadi how much time does one need to wait after I140 is approved but i485 is pending since Oct2020?
Why would you advise waiting for ead ap if H1B transfer can be done? I haven’t seen any updates on my biometrics for ead ap yet…
With regards to i485j supplement, is this something I should negotiate with new employer before accepting the offer? Many companies seem to have a cool down period of 6 months b4 they agree to start GreenCard process (that’s what I have learned)
Unless the previous employer pulls the pending I-140, you just need to submit a I-485J to show that it has been 180 pending days for your I-485 + your new job is similar to previous job. This is based on the previous employer not pulling your I-140. My suggestion would be go for premium processing on that pending I-140, get it approved and then transfer. That way your AOS will not be at risk of getting jeopardized.