Counterpart (2017–2019).
From Wikipedia:
Counterpart is an American science fiction thriller television series starring J. K. Simmons. It was created by Justin Marks and was first broadcast on the premium cable network Starz. The series ran for 20 episodes across two seasons. It premiered on December 10, 2017, and aired its final episode on February 17, 2019.
Howard Silk, a gentle, quiet office worker, has been working for a Berlin-based United Nations agency, the Office of Interchange (OI), for thirty years. His position is too low for him to be told what his work—exchanging apparently nonsensical messages—really involves. The OI oversees a checkpoint below its headquarters between parallel Earths (the "Alpha" and "Prime" worlds). The parallel Earths were created in 1987 during an experiment by East Germany when only a scientist named Yanek was on-site. The "Alpha world" Yanek met his "Prime world" counterpart, and they soon began studying how the initially identical Earths diverge.
The differences between the two worlds become more pronounced after 1996, when a flu pandemic killed hundreds of millions in the Prime world, setting back the world technologically but advancing it in life sciences. The virus was suspected of being purposely released by the Alpha world into the Prime world, which resulted in a tense cold war between the two worlds, with counterparts used as spies and sleeper agents. Silk's Alpha world continues to resemble ours, but the Prime world becomes quite different. Howard Silk Prime is a ruthless intelligence operative. Matters escalate during the series when a powerful rogue faction on Prime executes long-simmering plans to get revenge on Alpha.
