Boot to Internet Recovery and erase / install is the best path when any update happens. In the vast, vast majority of cases you will be fine and only Macs with T2 chip would need an assist to re-flash the EFI. Yours is amenable to target mode boot and all the normal ways to reinstall the OS when it’s not bootable from the internal drive.

Boot to Internet Recovery and erase / install is the best path when any update happens. In the vast, vast majority of cases you will be fine and only Macs with T2 chip would need an assist to re-flash the EFI. Yours is amenable to target mode boot and all the normal ways to reinstall the OS when it’s not bootable from the internal drive.

1. Reset the SMC one time - https://support.apple.com/en-us/HT201295
2. Internet Recovery would work for newer Macs - https://support.apple.com/en-us/HT201314 - your mac needs you to bring a bootable USB or drive to it or to connect in Target Disk Mode to another mac to image it / run the installer against your storage.