Well there is Splinter of the Mind’s Eye where Luke and Vader first fought, and Luke had a sort of almost romance with Princess Leia. Vader even appears to have fallen in a deep pit and died and he lost an arm.
Some fans posit that the Vader Luke and Leia fought in the Temple of Pomojema was a spectre created by the Kaiburr Crystal rather than the real Vader. Think Luke’s vision of Vader in the cave on Dagobah dialled up to 11. Obviously that wasn’t what Alan Dean Foster had in mind when writing the novel, but it’s the only real way you can integrate SOTME and TESB in the same continuity holistically.