This App will only work on GPUs that are Compute Capability 5.0 or higher.
See list of supported GPUs here, https://en.wikipedia.org/wiki/CUDA#GPUs_supported

The CUDA 9.0 App is for Sierra 12.4 and above, using a CUDA 9.0 or above driver.
The CUDA 10.2 App is for High Sierra with the last CUDA Driver.

If you wish to use 100% CPU per task, use the cmdline setting -nobs.
<cmdline>-nobs</cmdline>

Run One task at a time, there isn't any advantage to running more, and you will use twice or more of the vRAM.

Finish your existing GPU tasks, then place the expanded files in the /Library/Application Support/BOINC Data/projects/setiathome.berkeley.edu folder.
If you are not familiar with changing owners with the Terminal, just reinstall BOINC to set the correct owners/permissions.

As of Feb 13, 2020 there is a problem with running the v0.98 App on the NV GPU connected to a monitor, at some point the App will start Missing Pulses.
1) The best workaround is to use a dedicated NV, AMD, or Intel GPU to run just the monitor, set the monitor to never sleep, and tell BOINC to ignore that NV GPU. Some report connecting a monitor to All GPUs also avoids the problem.
2) The Best Method is after a reboot, connect the monitor cable to each NV GPU not connected to a monitor long enough to see the desktop appear, then connect the cable back to the dedicated GPU running the monitor, and start BOINC. Usually once BOINC is running there isn't a problem until the next reboot.
3) Further testing shows the problem doesn't happen when using a GTX 1080Ti, it's possible the plain 1080 may also work. Any other GPU with GDDR5 memory will have the problem with Missing Pulses after a reboot. I would suggest using only a 1080Ti to run the CUDA Special App on a Mac.

My 1080Ti Mac only has the Problem on the 1070s, I don't have any trouble with the two 1080Ti, https://setiathome.berkeley.edu/show_host_detail.php?hostid=6796479
