Catalina problem with my Mac mini 2018 + Razer Core X enclosure + RX480 GPU
I can only comment about Mojave.
Can confirm a similar issue with Radeon RX 580 8 GB in Sonnet enclosure on the newest macOS Catalina 10.15.6 Beta (19G60d).
The filesystem is encrypted, so I can see the first prompt to enter my password and later it stuck on the boot picture.
Inspecting system logs didn't add much insight into what is the problem.