A problem with the FXAA shader...
Please, start the viewer with ALM off, then enable "Debug GL" in "Advanced" -> "Rendering" -> "Render tests", and switch ALM on: the log should tell us what it does not like in the FXAA shader.
Also, you might be able to enable the SMAA shader instead (which is way better anyway)...
Hmm... We might be able to switch to OpenGL v4.1 then...
This could be done by replacing "NSOpenGLProfileVersion3_2Core" with "NSOpenGLProfileVersion4_1Core" line 244 of linden/indra/llwindow/llopenglview-objc.mm, and then finding the right GLSL version to use (lines 414 to 420 of linden/indra/llrender/llgl.cpp, maybe even disabling that block entirely with "#if LL_DARWIN && 0" line 412): starting the resulting viewer binary with "DebugGLOnRestart" set to TRUE from the previous (working) session would list the problem in the log, should the viewer window stay black.
Also, not changing for GL v4.1 in linden/indra/llwindow/llopenglview-objc.mm, you could try and disable the macOS workaround in linden/indra/llrender/llgl.cpp (using "#if LL_DARWIN && 0" line 412), and see what happens (that would use the shader language version advertised by macOS instead of limiting it to v1.40)...EDIT: I produced a version that can be switched at runtime between OpenGL v2.1 compatibility profile and Open GL core profile (v3.2 or 4.1, as macOS sees fit), by toggling the "Enable core GL profile" check box (and restarting the viewer) in the "Preferences" floater, "Graphics" tab, "GPU/GL features" sub-tab. It also limits GLSL to v1.20 for OpenGL v2.1 (as usual), v1.40 when the advertised OpenGL version is below v3.3 (as v1.30.2.6 did), and adopts whatever GLSL version advertised for OpenGL v3.3 and better: this should hopefully make macOS happy enough... I am sending you the URL of the sources tarball via a PM; please let me know how it fares for you.