Catalina 10.15.4 Supplemental update
@mini-i5, well, I just installed it (Mini 2018)... eGPU still boots to empty black screen and hangs about 50% of the time. Why can't Apple fix this mess?
I applied the 10.15.4 update successfully and purge-wrangler worked correctly. However, the 10.15.4 Supplemental update resets the csrutil setting to 'enabled'. You need to go into Recovery mode (cmd-R on boot) and set csrutil to 'disable'.