How to Choose the Best macOS Version for External Display with Thunderbolt connection will not work
The best upgrade is not always the newest release; it is the newest release that keeps graphics, Wi-Fi, sleep, battery and daily apps reliable. Unsupported Macs depend on OpenCore Legacy Patcher root patches, and each macOS release changes drivers, security policy and graphics behaviour.
Quick Checks
- Backup current state: Save a copy of your working EFI and run a full system backup before changing settings.
- Identify hardware components: Note down your exact CPU, GPU, Wi-Fi card, and motherboard/laptop model.
- Ensure utility alignment: Keep OpenCore, OCLP, and ProperTree updated.
Fix Steps
- Create a rollback point: Make a Time Machine backup and keep a copy of your last working EFI folder before editing OpenCore, kexts or root patches.
- Match macOS to hardware age: 2011-2012 Macs often behave better on Monterey or Ventura; 2013-2017 Macs can usually test Sonoma or Sequoia with an SSD and enough RAM.
- Avoid risky releases for production: Treat macOS Tahoe or any newly unsupported path as experimental until OCLP support is explicit.
- Update OCLP first: Install the latest OpenCore Legacy Patcher, build/install OpenCore, then run root patches after macOS boots.
- Test the real workload: Check browser tabs, Office/Adobe, printing, sleep, Wi-Fi, Bluetooth and battery before calling the upgrade successful.
- Keep a downgrade path: Have a USB installer for the previous stable macOS before upgrading.
Do Not Continue If
- Do not continue if: you do not have a working EFI backup, a Time Machine backup, or another bootable macOS installer.
- Stop and capture evidence: if the machine stops booting, take a photo of the last verbose line before changing more settings.
Verify It Worked
- The machine boots twice without manual intervention.
- Graphics acceleration and Wi-Fi work after root patches.
- The user apps that motivated the upgrade actually launch.
- Battery and thermals are acceptable for the intended workload.
Rollback
- Restore the previous macOS from Time Machine.
- Reinstall the older stable release with OCLP.
- Keep data on a separate backup before experimenting again.
Next Action
- Test now: reboot twice, reproduce the original problem, and confirm whether the same symptom returns.
- If it still fails: record the Mac model, macOS build, OpenCore or OCLP version, GPU, Wi-Fi/Bluetooth chipset, and the last visible error.
- Read next: use the related searches below for the nearest OpenCore or OCLP fix before making another change.
Related iATKOS Searches
- OpenCore · OCLP · EFI · kexts · config.plist · macOS troubleshooting
Original Question: "External Display with Thunderbolt connection will not work"
I am praying someone can please help me. I am in so far over my head and need help. I installed the latest OpenCore patch to try and get airplay activated on my Late 2015 Intel iMac. That part worked. But now for some reason the iMac's external displays will not be detected. I tried running the Post Install Root Patch through the app but it says they are all installed. I've restarted the machine and cleared the NRAM, I've tried plugging and unplugging the displays in every configuration at startup, before start up and after. Detect Displays will not show up. I am running the last supported version of Monterey, I wasn't interested in updating to Sonoma or any of that, just wanted airplay. These displays have worked for years with this iMac, this is the only change. Can anyone out there please point me anywhere I can get help on how to get these displays back or how to remove OpenCore and just get my Mac back to how it was before the install. Even if there is a paid service, I need to get this back operational.
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