Besides render texture being black sometimes full screen goes black. I have tested on mac. At the start of the video, when entering playmode, you can see the expected result in editor.

Repro steps:
1) Change manifest for your local SRP
2) Open project RT scene
3) Enter playmode see the object in front is not black
4) Build the scene and open
5) Either the object in front is black or the whole screen

Notes:
* Full screen does not go black if you build a scene without RT in this same project. For example SampleScene
* This case could be related to this forum post, however changing texture to B10G11R11_UFLOAT_PACK32 via UI still resulted in black render target
https://forum.unity.com/threads/hdrp-render-texture.792594/