I think there's a genuine spectrum between man-made bio-weapon (not very believable IMO), through gain of function research (I've read enough that - if true - the RNA evidence suggests that it probably wasn't this), through to leak from animal studies.
Gain of function, if it isn't ruled out by RNA or other approaches, isn't quite man-made and is at least somewhat plausible. Gain of function research on the flu is (as I understand it) how the flu vaccine is created ahead of the season.
Evans NG, Lipsitch M, Levinson M
The ethics of biosafety considerations in gain-of-function research resulting in the creation of potential pandemic pathogens
Journal of Medical Ethics 2015;41:901-908.
This paper proposes an ethical framework for evaluating biosafety risks of gain-of-function (GOF) experiments that create novel strains of influenza expected to be virulent and transmissible in humans, so-called potential pandemic pathogens (PPPs). Such research raises ethical concerns because of the risk that accidental release from a laboratory could lead to extensive or even global spread of a virulent pathogen.
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.
Gain of function, if it isn't ruled out by RNA or other approaches, isn't quite man-made and is at least somewhat plausible. Gain of function research on the flu is (as I understand it) how the flu vaccine is created ahead of the season.
https://jme.bmj.com/content/41/11/901
Evans NG, Lipsitch M, Levinson M The ethics of biosafety considerations in gain-of-function research resulting in the creation of potential pandemic pathogens
Journal of Medical Ethics 2015;41:901-908.
This paper proposes an ethical framework for evaluating biosafety risks of gain-of-function (GOF) experiments that create novel strains of influenza expected to be virulent and transmissible in humans, so-called potential pandemic pathogens (PPPs). Such research raises ethical concerns because of the risk that accidental release from a laboratory could lead to extensive or even global spread of a virulent pathogen.