Created bootable usb already but kept booting into the old MacOS

[tszkitc]

Just trying to Install macOS Sequoia on my 2017 4K iMac.
Boot screen select the usb bootable drive then straight boot the internal drive
which host the macOS Sonoma. It won't show the utilities screen.
Please enlighten me how to install??
Many Thanks.

 

[CoastalOR]

The maximum Apple supported macOS for a 2017 21.5 inch 4k iMac is Ventura (13). Apple does not support Sequoia (15) for your iMac.

 

[tszkitc]

I m using OCLP.
The computer already has Sonoma on it using OCLP.
I do not why not able to fresh install Sequoia.

 

[Bigwaff]

I do not why not able to fresh install Sequoia

Did you create the Sequoia installer using OCLP? You need to be very specific detailing steps you have taken so far.

 

[tszkitc]

Did you create the Sequoia installer using OCLP? You need to be very specific detailing steps you have taken so far.

I use OCLP to created a Sequoia installer and install OCLP on it already. When I reboot the computer, there are 2 EFI Boot in the menu. One is OLD and one is the new bootable usb. No matter which one I choose, the computer will boot into the OLD Sonoma OS.

 

[Bigwaff]

After you pick an EFI, you have to pick a startup disk. When selected, the Sequoia USB boots Sonoma?

 

[tszkitc]

After you pick an EFI, you have to pick a startup disk. When selected, the Sequoia USB boots Sonoma?

I only have one startup disk which is the internal 1TB Fusion Drive. No, the system never prompt me to choose a startup drive. Once selected the EFI, the system shown apple logo and boot into the Sonoma system. I tried to re-create the USB bootable drive but it didn't help.

 

[tszkitc]

Problem solved. I did not know I have to keep pressing the Option key when I am using cursor key to select the booting EFI. One more thing, I thought this is to freshly install a new OS. I did not know my thing in computer kept untouched. How do I erase everything on the Fusion Drive and install a new copy of Sequoia?? I tried booting into the recovery mode and select to erase the drive but it took very long and no progress shown.

 

[Bigwaff]

After picking the correct EFI and Sequoia Installer in boot picker, Sequoia installer should start. Use Disk Utility to erase your internal storage as GUID APFS. Then install Sequoia macOS. If you can’t erase from Sequoia Installer Disk Utility, then you will need to boot from a supported macOS installer USB media and use Disk Utility to erase your internal storage GUID APFS. Once erased, boot from the EFI Sequoia installer USB media

Update: In Disk Utility, select View > Show All Devices and erase after selecting the top most node in tree representing your internal storage.