Here Radeon™ RX 570 Drivers & Support
it is possible to find fire wood on this card and Ubuntu.
Specifically, the driver itself:
Radeon™ Software for Linux® Driver for Ubuntu 18.04.3
The link can not download, unfortunately.
Need directly from the AMD website.
Go to the first link at the top of the post.
Choose there, as in the screenshot and click on DOWNLOAD*
And this - the Radeon™ Software for Linux® Installation
instruction how to install it...