If you absolutely insist to have the latest AMD Radeon driver version you may use the PPA third-party repository which might be always ahead of the stable default opensource driver coming with your Ubuntu 20.04 system as default.

Install the latest stable version of the Mesa driver

Install the latest bleeding-edge version of the Mesa driver

Install the Ernst Sjöstrand - Mesa Almost Stable driver

Install the Ernst Sjöstrand - Mesa Unstable driver

https://launchpad.net/~kisak/+archive/ubuntu/kisak-mesa

https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers

https://launchpad.net/~paulo-miguel-dias/+archive/ubuntu/mesa

Ernst Sjöstrand Almost Stable Mesa driver

Ernst Sjöstrand Unstable Mesa driver