
die Rückkehr
return
The act of coming back to a starting point or home.
Nach langer Reise freute er sich auf seine Rückkehr in die Heimat.
After a long journey, he was looking forward to his return to his homeland.
return
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return
The act of coming back to a starting point or home.
Nach langer Reise freute er sich auf seine Rückkehr in die Heimat.
After a long journey, he was looking forward to his return to his homeland.

return
The restoration of a previous state or the resumption of a former activity.
Viele hoffen auf eine baldige Rückkehr zur Normalität.
Many people are hoping for a quick return to normality.
'Rückkehr' (return) is a noun derived from the separable verb 'zurückkehren' (to return). It is made up of 'Rück-' (from 'zurück', back) and 'kehr' (from the verb 'kehren', which here means 'to turn'). It describes the action of coming back.
Niemand rechnete mit seiner plötzlichen Rückkehr.
No one expected his sudden return.
The preposition after 'Rückkehr' (return) depends on the destination. You use 'nach' for places without an article (cities, countries), 'in' for places with an article, and 'zu' for states or activities.
Die Rückkehr nach Deutschland war für sie ein großer Schritt.
The return to Germany was a big step for her.
In the figurative meaning, 'Rückkehr' (return) is often used for the restoration of a previous state. Typical phrases are 'die Rückkehr zur Normalität' (the return to normality) or 'die Rückkehr in den Beruf' (the return to work).
Nach der Krise wünschten sich alle eine schnelle Rückkehr zur Normalität.
After the crisis, everyone wanted a quick return to normality.
comeback
Both words can refer to resuming an earlier activity after a break. Rückkehr is neutral, while Comeback places more emphasis on the public attention surrounding a person. Rückkehr suits a factual statement, whereas Comeback is more appropriate when there is strong public interest.

Nach zwei Jahren Pause kündigte die Sängerin ihre Rückkehr auf die Bühne an.
After a two-year break, the singer announced her return to the stage.
Nach zwei Jahren Pause feierte die Sängerin ein viel beachtetes Comeback auf der Bühne.
After a two-year break, the singer made a much-publicized comeback on stage.