This is Alina Chan, one of the co-authors of Viral: The Search for the Origin of Covid-19.
In defense of a natural origin of Omicron, this study describes the remarkable evolution of SARS-CoV-2 during convalescent plasma treatment of an immunosuppressed patient for 3-4 months; the mutations also reduced sensitivity to neutralizing antibodies: https://www.nature.com/articles/s41586-021-03291-y
We know that there is a large immunocompromised population in Africa and that Covid-19 is rampant there. We also know that most hospitals, regardless of country, don't have the resources to track the evolution of SARS-CoV-2 in their immunocompromised patients. So it's not unexpected that a variant like Omicron could have evolved over an entire year in an immunocompromised individual before finally infecting others.
If there is any evidence that a lab in the region was serially passaging SARS-CoV-2 in neutralizing antibodies/patient serum, then I'd say there is something to go on for a potential lab origin. But at the moment, there is not even circumstantial evidence pointing to this happening in Africa. Maybe setting up a secure channel for whistleblowers with evidence of the above would be the most productive approach.
The above is not to say that I don't think there needs to be much more transparency and accountability from scientists working with pathogens.
https://twitter.com/Ayjchan/status/1468582694007279616