the.com/backseat driver

means A passenger who criticizes or gives unsolicited instructions to the person actually driving — or, by extension, anyone who meddles in a task they aren't responsible for performing.

from Literal before it was figurative: the phrase comes straight out of early 20th-century motoring, when cars grew common enough that someone in the back seat could — and apparently always did — lean forward with opinions about the driver's speed, lane choice, or turns. The term was in use by the 1920s in American English, migrating quickly from literal car trips to any situation where someone with no hands on the wheel insists on steering anyway.