If the petition is approved while I’m in the U.S., do I need to go to the embassy for a visa? Or is that the adjustment of status (AOS) via Form I-485 — done without leaving the country? Who issues the visa then, and is a visa even necessary if you do an adjustment of status?
Visa and status are different things. If you file an I‑485, that’s an adjustment of status — everything happens inside the country without leaving. I did that myself after the petition was approved — I filed the I‑485, and all the documents arrived by mail. USCIS may call for an in‑country interview in about 5% of cases, but usually they don’t. Consular processing is a separate route; it’s chosen by people who are outside the U.S. or who for some reason want to obtain an immigrant visa through the embassy. But if you’re currently in the U.S. and have lawful status, it’s simpler and faster to go through the I‑485.
yes, that’s right — the I-485 is your path; you don’t need to get a visa.
The only thing I’ll add — your status must be legal as of the date you file the I-485, not the petition approval date. When I was sorting out my case, that was the first thing I checked. And once the I-485 is in the system, you can’t leave without advance parole, otherwise your application will be automatically withdrawn.