AMD isn't going to issue a press release to deny a rumour like this. AMD just told those from the press who asked that the rumour was nonsense.
Even a few weeks ago AMD higher-ups have said that Zen 3 is on track for release this year, and those higher-ups will know things a lot further in advance than rumour sources.
AMD are being tight-lipped about Zen 3 to encourage more Zen 2 processor sales. They are already in a strong position, so they don't want anyone to adopt a "wait for Zen 3" mentality.
If AMD had delayed Zen 3, it would be a big failure. AMD needs solid roadmap execution to gain market share within the server and notebook markets. They need to be reliable where Intel isn't.
So no, there isn't something to link to on AMD's website to deny this rumour. We just have all of the statements from AMD from earlier this year that they are committed to releasing Zen 3 in 2020. AMD wants us to take them at their word.