armchair critic

armchair critic (plural armchair critics)

1. A person who makes criticisms on a subject they have little knowledge of or practical experience in.
   • 2021 March 14, Vikram Dodd, Aamna Mohdin, Aubrey Allegretti, “Cressida Dick refuses to quit over vigil policing and dismisses 'armchair critics'”, in The Guardian‎:

     Britain’s most senior police chief defied pressure to resign as she dismissed “armchair” critics amid widespread outrage over officers manhandling women who were mourning the killing of Sarah Everard.

The use of "armchair" is figurative, as though seated in an armchair.

• armchair criticism

• “armchair critic”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.