P: Colored "pixel" artifacts/subdued blacks in shadow areas (older Macs) (also visible on CR)

I reported this too on an earlier posting.  I went thru all of the troubleshooting  steps that were suggested in a reply re the graphics processor.  I shut off accelerated put it back on etc. The testing only confirmed that the Radeon Graphics chip is error free. I know it is 8 yrs old,, and the manufacturer no longer supports it, but it worked fine until I installed and started using LR classic the week of Oct 26 2023.   This would seem to indicate that (given the big number of reports of similar clipping and freezing of masks) that Adobe should fix this problem for its users. The masks are unusable.  
Worse for me, I can't replace the graphics card. I thought it was possible to do, but it is attached to the mother board in my late 2015 Imac retina 5 k 27 inch computer.   It is infathomable that a bug in code that should be fixable should result in making the entire machine unusable for 1 program, while  great for all others. 

Adobe should fix these problems it is almost as if they took the LR software out of the oven before it was baked. 

thanks

This is probably my issue!

Yes! This is exactly what is happening to me! I heard back from the preset company in my attempt to isolate the issue and they said it must be a lightroom 13. They ran it on an older lightroom and there was no problems. Unfortunately for me, I didn't catch this soon enough and I'm re-editing work! 

@lindseyanne78 reinstall the version 12 

What is or computer look on menu 🍏.

you are not allone with this problem.

look my post 

Hello! I can't get my shadow clippings to turn off, or whatever this is that's showing up in develop. It shows up when I edit, and also shows up when I download and is in the final image. HELP! This just started happening a month ago! I've done all the updates. It's hard to see in these images, but it's some kind of banding? It's only ever in the shadows. If there is a way to turn this off I would very much appreciate the help!

Indeed there is an export issue too when the image in blacks looks like inferred, randomly happens. 

I don't know what happened to these photos. The original photo file is normal, except for color adjustments. There was a strange color appearing in the picture. I don't know what caused it and how to fix it. Does anyone know how to fix it? Please help me.

you can set Preferences > Performance > Use Graphics Processor to Off or roll back to LR 12.5.

I think you'll find 12.3 is the safest bet.  I've seen GPU problems in every version I've tried since 12.4.

Si on enlève le processeur graphique cela ne change rien sur le 12 ou 13.

ce qui est bizarre c'est que même à l'exportation en tout cas pour moi j'ai ce problème d'artefacts sur le 13

Personnellement j'avais ce problème sur le 12 mais aucun soucis à l'exportation, donc est bien du à bug!!

j'espere que cela va s'arranger car mon mac fonctionne parfaitement avec Capture One!

ps: pour la capture d'écran je l'ai fait à partir du 12 car j'ai vraiment pas envie de réinstaller à nouveau le 13.

@nealedel, you've got a ten-year-old graphics processor that's no longer receiving bug fixes from AMD. It's possible, though perhaps not likely, that a future version of LR will avoid this problem. Meanwhile, you can set Preferences > Performance > Use Graphics Processor to Off or roll back to LR 12.5  12.3.