All changes to a "document" are disabled

[brkorb]

It doesn't matter which tool I use, I can no longer make changes to the image.

I started with 8 stacked images and aligned them.

Next, I duplicated the layers, de-selected the originals and then blended the copies.

That was the end of my ability to change the image.

I cannot paint on any layer or layer mask, even newly created ones.

Same for healing brushes. And filters. Solid color layer. Anything. It has become immutable.

I've saved it as a 4GB TIFF, if anyone at Adobe wants a peek.

Oh, the layers are all 100% visible and normal and I did reset my brush, just in case. No go.

[brkorb]

Lovely. The TIFF file will do no good. Reopening the file and it all works. PS got itself into an internal state of confusion but didn't know it was confused. I could try to reproduce this, but I don't get paid for debugging software anymore. Mark this as a one-off until others complain.

Just to be clear:

Platform: iMac running Catalina (10.15.20) quad core i5 w/ 40GB RAM

Photoshop: 21.0.2 CC

Data: over SMB hosted on Linux with EXT4/RAID-1 underneath