GPT overwritten by Windows 8 Update

Hello,

Three years ago or so, I installed Windows 8 using Boot Camp. Earlier this week, I tried to switch back to Windows from Mac OS (High Sierra), and ran into a "no bootable device" error.

I followed the steps outlined in this post to create a hybrid MBR/GPT. This solved the problem. I was able to switch back and forth between Windows and Mac OS several times.

Today, I shut down Windows intending to boot back up in Mac OS. As Windows shut down, it "installed updates." I then discovered that my Macintosh HD boot volume had disappeared. I cannot boot into Mac OS.

My GPT seems to have changed. This is what it looked like before I edited the MBR:

And here is what it looks like now:

As far as I can tell 1) my recovery partition has disappeared and 2) my Macintosh HD partition has the wrong type (as represented by that long GUID). Can I change these things using the "gpt" tool without affecting the contents on disk, i.e. using "gpt remove" and "gpt add"? I do not have recent backups of my files.