While it would’ve been cool to see the world of Dark expand into 1899, the two series aren’t connected — meaning that they don’t share any characters or plot similarities. However, there is an opportunity to connect their worlds. Dark takes place over several time periods, as it travels forward and backward in time, and spans over 160 years. Its final season actually takes place in 1888, just 11 years before 1899. Naturally, Dark fans speculated that 1899 could easily be connected to its predecessor.
Source: https://www.distractify.com/p/is-1899-connected-to-dark