Ask them to define "Marxist"... for most people, it's just a "scary word" and dog whistle. It's worth remembering that MLK was labeled a Marxist as an attempt to discredit him as well- it's this year's version of "socialist".
"Critical Theories" emerged from the German Frankfort School, and were influenced by Social Marxist thinking (particularly in regards to power differentials). Additionally, the work of Freud and Erich Fromm were involved here (but no one says CRT is Freudian, which seems to be a significant slip). The second phase of Critical Theory, though, included some efforts to shift away from Marxism out of a desire to include a moral or ethical context (Marxism being agnostic/atheistic).
If you're a podcast person, this one opens up with a pretty good description of critical theory and where/when it diverged: https://www.christianitytoday.com/ct/podcasts/quick-to-listen/critical-race-theory-racism-evangelicals-divided-podcast.html (NOTE- that's from an evangelical perspective, the Marx discussion starts around 6:45)
Interesting article from the American Bar Association: https://www.americanbar.org/groups/crsj/publications/human_rights_magazine_home/civil-rights-reimagining-policing/a-lesson-on-critical-race-theory/