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
NOTE: Alternative drivers can also be considered, including: