Up to the end of 2020 how many humans had died in space?

After the landing of Apollo 11 on the Moon in 1969, the USSR began shifting the emphasis of its crewed space programme to orbiting space stations, with a view to a possible lunar landing of its own later in the 1970s. One other motivation for the shift in emphasis was to steal a march on the US Skylab programme then in development.

Salyut 1 was an early result of this programme and became the world's first space station. It was launched into low Earth orbit by the Soviet Union on 19 April 1971 and was followed by six more Salyut stations.

Shortly after the successful launch of Salyut 1 there followed the attempt to send a crew to it. Soyuz 10 was launched on 22 April 1971 as the world's first mission to the world's first space station. The docking was not successful because of latching problems: the crew returned to Earth without having entered the station. A new attempt was made with Soyuz 11 and it turned out to be the only crewed mission to board Salyut 1. The crew, Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev, arrived at the space station on 7 June 1971 and departed on 29 June. The photograph in the question is an extremely rare view of the world's first space station, as seen from the departing Soyuz 11.

However, the Soyuz 11 mission ended in disaster: the crew capsule depressurised during preparations for re-entry, killing the three-man crew. Until the end of 2020 the three crew members of Soyuz 11 were the only humans to have died in space.