I activated my visa at the border. They no longer put the I-551 stamp in the passport. The visa itself now has the annotation SERVES AS TEMPORARY I-551 EVIDENCING PERMANENT RESIDENCE FOR 1 YEAR. Next to the visa, they place a regular small blue entry stamp with the date of entry, and that is sufficient for re-entering the border. That’s what the officer told me.
Also, a bit about my interview experience:
I applied under the EB-2 NIW category. I prepared and brought every possible document with me. I also prepared answers in my head for any possible questions and carefully reread my entire case. However, the officer who interviewed me did not ask anything except who I work as and what I do at my job. There were a few basic mandatory questions, some small talk, and he wished me good luck in the U.S. at my new place. He was very polite. Everyone at the consulate was very polite.
The stress that lasted 3 years is finally over.
Thank you to everyone who gave advice. This forum is a wonderful place.