I have reason to believe that if the outgoing administration claims to have reason to believe something but refuses to provide the evidence behind it, they are lying.
https://twitter.com/CT_Bergstrom/status/1350292056782954498
Here's a very serious, legitimate review of the possible origins of SARS-CoV-2: https://www.nature.com/articles/s41591-020-01205-5
Unfortunately, from my experience, most people are going to believe what they want to believe, based more on political affiliation more than anything else, and the empirical facts don't register too strongly.
"Gain-of-function research is also subject to intense scrutiny and governmental oversight, precisely because of the high risk involved in conducting it safely; thus, it is extremely unlikely that gain-of-function research on hard-to-obtain coronaviruses (such as bat SARS-like coronaviruses) could occur under the radar."
This research was not happening under the radar. WIV has been openly publishing gain of function research on bat Coronaviruses for years. It's quite possible that SARS-CoV-2 was a research project that they fully intended to publish, but was accidentally released during the research.