Spent hours trying to get a "mining only" RX570 to crunch. Finally gave up. Guess what happened after I pulled the "mining only card"?" None of the other cards worked on boinc!
Tried default=1 in grub.

Ran /usr/bin/amdgpu-pro-uninstall
then to be sure did apt purge amdpro*

Then did (with and w/o the --compute)

sudo ./amdgpu-install --compute
on amd driver 19.50 (the lastest)

saw several error messages, dkms was mentioned along with the error:

void found where constant char expected

grep in /var/log showed error messages such as "amdgpu accelerated=0" which was duplicated in the
/var/bin/boinc/stderr... log file

Shut it down and the next morning did all the above except the following change

sudo ./amdgpu-install --OpenCL=legacy,pal --no-dkms

that worked, did not see the "void found where constant char expected" and boinc is crunching away

I am afraid to reboot. I do have default=1 in grub because I thought that might fix the problem but it seem the --no-dkms was what fixed the problem