I have heard some rumors that you can double AMD GPU hashrate using the experimental drivers in Ubuntu using the proprietary AMD mining drivers. I found some documentation that helped me to put a procedure together to accomplish this:
https://www.blog.albertbling.com/posts/how-to-mine-ethereum-on-linux/ <- albert's put together a great procedure to get the driver up and running on your card. I wouldn't follow his advice regarding upgrading though. I avoid that step.
I found with a fresh copy of 20.04 LTS, the driver install failed. I found on Reddit a procedure to patch this up in the comments here. Instead of following through Albert's blog I just installed Ubuntu, enabled security updates and didn't bother upgrading. I made sure to grab the old original 20.04 release as it really doesn't like the new kernel http://old-releases.ubuntu.com/releases/20.04.0/
I got it working and found that after setting up the beta 2004 release and following albert's guide (sans upgrade) it was able to configure the AMD mining (compute) drivers, which ended up doubling my hashrate when running SRBminer
ETH 0x9778efD459A908Ea273e8985a50e99a20970Ee82 <- feel free to donate if this helped you
Thanks, just getting started!