Is there a way to tell if Excel is still working or frozen?

I told Excel to copy down about 20 columns to 600,000 rows. Shortly after, it went to "Not responding," and it's been there for over three hours. I've seen it be "Not responding" before and then return with the result. But I don't know if I should keep waiting or abort and try something different. It's in manual calculation mode, so it should not be calculating, just copying cells.

Task Manager says Excel is using about 20% of CPU and it looks like the memory used has declined from around 3,000 Mb to about 1,000 Mb. The computer has 16 Gb of RAM.

Is there anything else I can look at to see if Excel is actually still working on it or is frozen and will never finish?

I'm in Windows 10 Pro 64 bit, running Office 2019 Pro (local version, not online).