HayleyHoughton wrote:
It wasn't already installed. It said last update was in 2020. I'm not sure of the version I installed as it won't let me in now to look.
Whatever the latest one I guess?
Where was that said in original question ??
Since it appears this may Actually be an upGRADE , which is much different than an upDATE - suggest shutdown the computer by whatever means required including Power Button. Disconnect all external devices. Connect to charger. Restart the computer in >>>> Safe Mode <<<<<.
Safe Mode will do a Repair Disk, clear cache files and only load Apple Software, extension and Fonts so loads slowly - Normal. It can take up to 10 or more minutes to eventually start and it may or may not allow the upGrade process to complete - hopefully successfully.