This is not true. Ralph Baric developed (and patented) a seamless technique to assemble coronaviruses in 2002 [1]. Baric was a close collaborator of the Coronavirus group at WIV.
Since then there has been even more progress. Since 2015 or so it's been possible to "print" DNA of any sequence.
In fact as COVID started to spread in China and the sequence was released, a Swiss lab used this technology to print the genome of SARS2, inject it into some yeast cells, and voila, you have the virus. They wrote this up in Nature [2].
If you wanted to change a naturally sampled virus using this technique, say, to insert a Furin site, swap out an RBD, whatever, you can literally do it with a text editor and copy and paste.
Since then there has been even more progress. Since 2015 or so it's been possible to "print" DNA of any sequence.
In fact as COVID started to spread in China and the sequence was released, a Swiss lab used this technology to print the genome of SARS2, inject it into some yeast cells, and voila, you have the virus. They wrote this up in Nature [2].
If you wanted to change a naturally sampled virus using this technique, say, to insert a Furin site, swap out an RBD, whatever, you can literally do it with a text editor and copy and paste.
[1] https://patents.google.com/patent/US7279327B2/en
[2] https://www.nature.com/articles/s41586-020-2294-9