Cant import in Photos now after OS UPDATE

I can't tell what question you might be asking, so I'll just throw some stuff out:

You say your are using macOS 12.12 Sierra on your iMac, is that true?

Apple recommends that you keep at least 10% or your hard drive space free. I try to use less than 85% of mine. How does your hard drive look? Have you tried to free up space? What happens then?

Where is your Photos Library located? Is it in your Pictures folder? Are you using iCloud Photos to synchronize pictures on your devices? In Photos>Settings>iCloud, do you have "Download Originals" checked, or is it "Optimize Storage?"

Let us know what's goin on and what you want to know, so we can help...

First, what I said about having more than 10% free space applies to your internal drive on you Mac. The Mac uses the drive to swap information around, and it needs that space. It's not about the external drive.

So it sounds like your external drive is not formatted properly. Did you do what it said and check the format of the drive? Often, external drives come formatted in ExFat format which is not compatible with Mac Photos. Sometimes it will try to work, but then corrupt the Photos Library, so newer OSs now check for that. As long as the Photos Library is on an improperly formatted drive, Photos will not work.

Use the app "Disk Utility" to help you out. You may be able to partition your drive so that half of it is formatted in APFS, and then you can copy the Library there.

Let us know....