Elementary is based on Ubuntu 18.04 and use an old Kernel (5.4). The only way for me to use my Bluetooth devices was upgrade to newest kernel (5.13.4)
Add the repository:
echo 'deb http://deb.xanmod.org releases main' | sudo tee /etc/apt/sources.list.d/xanmod-kernel.list
wget -qO - https://dl.xanmod.org/gpg.key | sudo apt-key --keyring /etc/apt/...
One thing I noticed while going through this old system was that it only had 2GB of RAM. I happened to have some memory laying around that worked for this system and after upgrading it to only 4GB of RAM and booting it up the 550RX fired right up.
It appears that this GPU needs more than 2GB of system memory to function.
Not receiving any replies, I plunged ahead on my own with the solution offered by Michael Wadman, Resolving my DNS Issues--Disabling systemd-resolved on Ubuntu 18.04.
Initially, this was clearly a partial solution—my manual edit only survived until my system went to sleep. When I woke it up, NetworkManager overwrote /etc/resolv.conf with one entry: