We have this problem on both comptures. Same specs, one is running High Sierra, one Catalina.
Both computers are connected to two EIZO EV2216W with default resolution.
On both computers Rhino mac 5 runs like a cat with no graphic or performance issues at all, as well as does other software (Blender 2.82, Affinity Photo - Designer - Publisher, Maxwell Render v.5)
Here is computer n.1
Rhino 6 SR26 2020-5-26 (Public Build, 6.26.20147.06482, Git hash:master @ 7788f6214ee9335d5793cc6177985a1c745e663b)
License type: Commercial, build 2020-05-26
License details: Cloud Zoo. In use by:
Apple Intel 64-bit macOS Version 10.15.5 (Build 19F101) (Physical RAM: 16Gb)
Mac Model Identifier: Macmini7,1
Machine name: zerododici’s Mac mini
Language: en-IT (MacOS default)
Intel Iris OpenGL Engine (OpenGL ver:4.1 INTEL-14.6.18)
OpenGL Settings
Safe mode: Off
Use accelerated hardware modes: On
Redraw scene when viewports are exposed: On
Anti-alias mode: 4x
Mip Map Filtering: Linear
Anisotropic Filtering Mode: Height
Vendor Name: Intel Inc.
Render version: 4.1
Shading Language: 4.10
Maximum Texture size: 16384 x 16384
Z-Buffer depth: n/a
Maximum Viewport size: 16384 x 16384
Total Video Memory: 1536 MB
Graphics: Intel Iris
Displays: EV2216W (90dpi 1x), EV2216W (90dpi 1x)
Graphics processors
Intel Iris (1536 MB)
EV2216W (1680 x 1050)
EV2216W (1680 x 1050)
USB devices
Apple, Inc.: IR Receiver
Apple Inc.: Bluetooth USB Host Controller
Apple Inc.: Apple Keyboard
Logitech: USB-PS/2 Optical Mouse
Bluetooth devices
None
Third party kernel extensions
None
Third party plugins
/usr/lib/swift/libswiftCore.dylib
/usr/lib/swift/libswiftCoreFoundation.dylib
/usr/lib/swift/libswiftCoreGraphics.dylib
/usr/lib/swift/libswiftDarwin.dylib
/usr/lib/swift/libswiftDispatch.dylib
/usr/lib/swift/libswiftFoundation.dylib
/usr/lib/swift/libswiftIOKit.dylib
/usr/lib/swift/libswiftObjectiveC.dylib
/usr/lib/swift/libswiftXPC.dylib
/usr/lib/swift/libswiftCryptoTokenKit.dylib
/usr/lib/swift/libswiftos.dylib
/Users/0xii/Library/Application Support/McNeel/Rhinoceros/MacPlugIns/maxwell_rhino.rhp/libmwdotnet_native.dylib
/Applications/Maxwell Render 5/libmxcommon.dylib
/Applications/Maxwell Render 5/libcudart.10.1.dylib
/Applications/Maxwell Render 5/extensions/wireframetexture.osx.mxx
/Applications/Maxwell Render 5/extensions/LensExtensions.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellCloner.osx.mxx
/Applications/Maxwell Render 5/libboost_date_time.dylib
/Applications/Maxwell Render 5/libboost_system.dylib
/Applications/Maxwell Render 5/libboost_filesystem.dylib
/Applications/Maxwell Render 5/libboost_iostreams.dylib
/Applications/Maxwell Render 5/libboost_thread.dylib
/Applications/Maxwell Render 5/extensions/xritebrdf.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellProcedurals.osx.mxx
/Applications/Maxwell Render 5/extensions/TiledTexture.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellHair.osx.mxx
/Applications/Maxwell Render 5/extensions/MGrassH.osx.mxx
/Applications/Maxwell Render 5/extensions/MGrassP.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellGrass.osx.mxx
/Applications/Maxwell Render 5/extensions/SubdivisionModifier.osx.mxx
/Applications/Maxwell Render 5/libmwglew.dylib
/Applications/Maxwell Render 5/libmwtbb.dylib
/Applications/Maxwell Render 5/extensions/MaxwellSea.osx.mxx
/Applications/Maxwell Render 5/extensions/Substance.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellScatter.osx.mxx
/Applications/Maxwell Render 5/extensions/AssetReference.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellVolumetric.osx.mxx
/Applications/Maxwell Render 5/libmwtbbmalloc.dylib
/Applications/Maxwell Render 5/extensions/MWObjectAlembic.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellMesher.osx.mxx
/Applications/Maxwell Render 5/extensions/MaterialModifiers.osx.mxx
/Applications/Maxwell Render 5/extensions/TableBrdf.osx.mxx
/Applications/Maxwell Render 5/extensions/rfmeshes.osx.mxx
/Applications/Maxwell Render 5/extensions/MaxwellParticles.osx.mxx
/Applications/Maxwell Render 5/extensions/rwmeshes.osx.mxx
/Users/0xii/Library/Application Support/McNeel/Rhinoceros/MacPlugIns/maxwell_rhino.rhp/libmxdotnet_native.dylib
/usr/lib/log/liblog_network.dylib
Rhino plugins
/Applications/Rhinoceros 2.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RhinoCycles.rhp “RhinoCycles” 6.26.20147.6482
/Applications/Rhinoceros 2.app/Contents/PlugIns/NamedSnapshots.rhp “Snapshots” 6.26.20147.1002
/Applications/Rhinoceros 2.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/GrasshopperPlugin.rhp “Grasshopper” 6.26.20147.6482
/Users/0xii/Library/Application Support/McNeel/Rhinoceros/MacPlugIns/maxwell_rhino.rhp “Maxwell for Rhino” 5.1.6.1
/Applications/Rhinoceros 2.app/Contents/PlugIns/PanelingTools.rhp “PanelingTools” 6.26.20147.1002
/Applications/Rhinoceros 2.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Commands.rhp “Commands” 6.26.20147.6482
/Applications/Rhinoceros 2.app/Contents/Frameworks/RhMaterialEditor.framework “Renderer Development Kit” 6.26.20147.1002
/Applications/Rhinoceros 2.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RDK_EtoUI.rhp “RDK_EtoUI” 6.26.20147.6482
/Applications/Rhinoceros 2.app/Contents/PlugIns/Displacement.rhp “Displacement” 6.26.20147.1002
/Applications/Rhinoceros 2.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RhinoDLR_Python.rhp “IronPython” 6.26.20147.6482
/Applications/Rhinoceros 2.app/Contents/PlugIns/RhinoRender.rhp “Rhino Render” 6.26.20147.1002