Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.51
Broken: version: 2.91.0, branch: master, commit date: 2020-11-25 08:34, hash: rB0f45cab862b8
Short description of error
Can't use this specific matcap
Exact steps for others to reproduce the error
Create a new scene, go to preferences/lights/matcap and import the attached file.
Now you should see the imported matcap in the list, but it won't show in viewport.