What they'd most likely output is a "report" with "findings" that "point to" or "suggest" certain things like bad protocols or insecure procedures or disconnected safety sensors etc. Hardly evidence, and not really actionable even if they were allowed to get there and eventually publish it.
This is the same kind of crap as with the "election" report in the US. They couldn't find hard-evidence because despite this being 2020, camera's aren't everywhere, evidence isn't readily available, and not everyone is keep ridiculous-level audit logs and collating as much info as we want. All they eventually put in their report were discrepancies, not-installed windows updates, internet-connected machines, etc. No smoking gun, and understandably so because even if it did happen, there is no easy and straightforward way to prove it.
The WHO team wasn't even allowed near the labs, much less enter it. They got a very curated tour of Wuhan (which isn't surprising).