macOS Big Sur on Apple M1

This sounds like something else possibly not related to M1 is happening here. @dean.cameron please run the SystemInfo command in Rhino and paste the results here.

Side note until a native version of Rhino is available - according to this link:

DaVinci Resolve update brings 3x faster M1 Mac performance along with 30% longer battery life - 9to5Mac

having applications run natively can make a huge difference. Was kind of obvious, but 3x sounds pretty sweet!

sure here are the results
Rhino 7 SR9 2021-8-10 (Rhino 7, 7.9.21222.15002, Git hash:master @ 190335c3fb65efe86c302714a8959a7dadfe667b)
License type: Evaluation, build 2021-08-10
License details: Stand-Alone
Expires on: 2021-10-26

Apple Intel 64-bit macOS Version 11.5.1 (Build 20G80) (Physical RAM: 8Gb)
Mac Model Identifier: Macmini9,1
Language: en-AU (MacOS default)

Apple M1 (OpenGL ver:4.1 Metal - 71.7.1)

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: High

Vendor Name: Apple
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: 5461 MB
Graphics: Apple M1
Displays: Unknown (94dpi 1x)

Graphics processors
Apple M1
LED Cinema Display (1920 x 1200 @ 60.00Hz)

USB devices
VIA Technologies Inc. : USB 2.0 BILLBOARD
Logitech: G300s Optical Gaming Mouse
Blue Microphones: Yeti Nano

Bluetooth devices
Cambridge Silicon Radio: AudioWear, AudioWear Voice, ARfcomm, Hands-Free unit, SPP Dev, Wireless iAP, Headset
Apple: Apple Wireless Keyboard

Third party kernel extensions
None

Third party plugins
/usr/libexec/rosetta/runtime
/Library/Apple/usr/libexec/oah/libRosettaRuntime
/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/libswiftOSLog.dylib
/usr/lib/swift/libswiftObjectiveC.dylib
/usr/lib/swift/libswiftXPC.dylib
/usr/lib/swift/libswiftos.dylib
/usr/lib/swift/libswiftAppKit.dylib
/usr/lib/swift/libswiftCloudKit.dylib
/usr/lib/swift/libswiftContacts.dylib
/usr/lib/swift/libswiftCoreData.dylib
/usr/lib/swift/libswiftCoreImage.dylib
/usr/lib/swift/libswiftCoreLocation.dylib
/usr/lib/swift/libswiftMetal.dylib
/usr/lib/swift/libswiftQuartzCore.dylib
/usr/lib/swift/libswiftUniformTypeIdentifiers.dylib
/usr/lib/swift/libswiftsimd.dylib
/usr/lib/swift/libswiftAccelerate.dylib
/usr/lib/log/liblog_network.dylib

Rhino plugins that do not ship with Rhino

Rhino plugins that ship with Rhino
/Applications/Rhino 7.app/Contents/PlugIns/NamedSnapshots.rhp “Snapshots” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/PlugIns/PanelingTools.rhp “PanelingTools” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/PlugIns/AnimationTools.rhp “AnimationTools” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/Frameworks/RhMaterialEditor.framework “Renderer Development Kit” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/PlugIns/Displacement.rhp “Displacement” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/PlugIns/RhinoLabsTools.rhp “Rhino Labs Tools” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/PlugIns/RhinoRender.rhp “Legacy Rhino Render” 7.9.21222.1002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Commands.rhp “Commands” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Import_OBJ.rhp “Import_OBJ” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/export_XAML.rhp “export_xaml” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/QuadRemesh.rhp “QuadRemesh” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Export_OBJ.rhp “export_OBJ” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RDK_EtoUI.rhp “RDK_EtoUI” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/export_SVG.rhp “Export SVG” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/MeshCommands.rhp “MeshCommands” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Export_DAE.rhp “Export_DAE” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/export_PDF.rhp “PDF Export” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/export_IGES.rhp “IGES Export Plug-in” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Import_SVG.rhp “Import_SVG” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/BlockEdit.rhp “BlockEdit” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Export_AMF.rhp “Export_AMF” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RhinoRenderCycles.rhp “Rhino Render” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/import_DST.rhp “Import_DST” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/export_PLY.rhp “PLY - Polygon File Format Export” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/Import_AMF.rhp “Import_AMF” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RhinoCycles.rhp “RhinoCycles” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/RhinoDLR_Python.rhp “IronPython” 7.9.21222.15002
/Applications/Rhino 7.app/Contents/Frameworks/RhCore.framework/Resources/ManagedPlugIns/GrasshopperPlugin.rhp “Grasshopper” 7.9.21222.15002

Thanks for that SystemInfo data, Dean.
You never answered Brian’s question about the files. Are you just launching Rhino and then it takes a long time for the splash screen to appear or are you directly opening a specific file from, e.g., Finder?
-wim

no Im launching rhino by opening a reasonable sized file

What happens if you start Rhino by itself without opening a file?