Hi there, we had our final interview March 14 and received our passports with visas back on March 24. The consular processing updated to ‘issued’ on Mon, March 17. The issue is that the usual pickup location in London (DX) closed down and it’s been transferred to Mail Boxes collection point - they are extremely disorganised and do not have a system in place to manage the enormous undertaking. If you can, I would perhaps suggest asking for it to be mailed to you vs. pickup - if you do it that way, I wouldn’t be surprised if you get it sooner. Otherwise you just have to be patient.
as for when you enter the country the first time on your Immigrant Visa, you will be given a visa package that is sealed and which you need to hand to the Customs officer when you’re entering for the first time. They will open it, see the embassy’s paperwork and allow you through. From there, you need to fill out specific info on a website to have your greencard card mailed to you when you land in the US.
Hope this helps.