It's just a plug-in. Go to the folder where the plug-in is located and delete it.
where is this folder?
That's what I can not find (hence my question on this forum)
I suspect your question is your trying to fix something you perceive is wrong and have decided that uninstalling ACR 10.4 will fix it, or you'd like to see if it fixes the issue.
What is the underlying issue or situation that lead you to believe uninstalling ACR 10.4 is a good idea, which it is likely not?
Is it causing app-errors (turn off the GPU in ACR preferences not PS preferences), or are non-raw files you want to open in PS are opening in ACR on the way into PS and you don't want this extra step (turn off JPG, HEIF, TIF file handling in ACR preferences), or are you under the mistaken impression that uninstalling ACR 10.4 will put ACR 10.3 back, which it won't?
If you indeed want to delete the ACR 10.4 plug-in, then rather than deleting it, I'd suggest you rename it to have a name that doesn't end in .8bi (like 8bb or 8bi_) so you can easily put it back in service once you find out uninstalling (deleting) it wasn't the right idea.
yes indeed ACR 10.4 literally blocks my computer when I want to open a RAW file of my D850. Also I would like to install a previous version of ACR.
But I can not locate where this plug-in is located in order to uninstall it.
The question should be asked, why you're running such an old OS on your Mac. 10.15.x is the current version, I think. If your Mac is so old it won't support the newer OSes that might be what ACR is having an issue.
Try this: go to PS Preferences / Camera Raw Preferences (not just PS Preferences) and try turning off the Graphics Processor (GPU) or turn it on if it's off, and see if you can get past the block, although if you have a high screen resolution then you'll likely need it turned on for speed, but experiment to see if it changes.
Also, I think the D850 is supported by ACR 9.12.1 and there happens to be an installer for that on this page, so try running that:
thanks ssprengel. I still do not know how to uninstall ACR but I changed the ACR preferences in Photoshop (turning off the Graphics Processor (GPU)) and now ACR no longer blocks my computer when I open a RAW file of my D850, D3 or D800.
Many thanks to you and thank you for your investment in my problem and to find a solution so quickly !! Again, thank you very much