Quick answer: Unity UI Toolkit RenderTexture displayed in an Image element disappearing when wrapped in a Mask? Mask uses depth pass; conflicts with RT - use ClipChildren instead.
Mini-map in a circular mask; visible without mask; black inside the mask.
Use ClipChildren
style.overflow = Hidden + style.borderRadius = circle. Effectively masks without depth pass.
Or rebuild as stencil
Custom Mask with stencil; works for RT but heavier.
Audit Mask usage with RT
RT-displaying elements; Mask interactions. Document.
“Masks and RTs use different passes. Combination has edge cases.”
For RT in UI, the ClipChildren overflow trick is the safe pattern. Document; reuse.