The original right/left was Nazi vs Bolshevik. When the Nazis lost the bolsheviks, American and European socialists took to calling any opposition “right wing.”
They call anyone they disagree with a “Fascist”.
The original right/left designation was the Paris Senat 250- 210 years ago. The royalists sat on the right of the chamber, the revolutionaries on the left.
The Nazis, the Fascists, and the Communists were all leftists.
The Communists only painted them as “right wing” as a means of discrediting them within the left. No different from Mao’s “anti-rightist” campaign, where he purges a bunch of communists from the CCP.
After WWII the American Left used this to paint them as rightwing so as to smear the American Right, and to disassociate themselves from them. Even though the American Left loved Hitler and Mussolini prior to WWII. (Hitler was Time Man of the Year, and FDR praised Mussolini in his letters)