I had 10.15.5 working great on my rig with Ryzen 9 3900x, 32 GB 3200 MHz RAM, Asus X570-p, fast NVMe and RX 580 GPU.
This morning, I stopped having OC in my reFind bootloader for unknown reason and the whole thing is weird, jittery, stuttering GPU, slow, almost like on a spinning HDD...