Some techniques of manipulating the virus would leave "fingerprints". Others would not. My understanding is that the sweeping assertions that COVID-19 would show clear signs of being manipulated have been largely debunked. Many ultimately traced back to a letter written by a group of virologists led by Kristian Andersen and published in Nature, but all that letter did was assert that some techniques (not all!) were unlikely (but even then, not impossible).

I'm unaware of any reputable experts who are willing to assert that manipulation via, eg, serial passaging, can be ruled out. The closest you'll get is assertions that a natural zoonotic origin is, in their estimation, more likely.

See, eg, https://nymag.com/intelligencer/article/coronavirus-lab-esca... and https://nicholaswade.medium.com/origin-of-covid-following-th....