I recently had to re-install all programs on my PC, hence I have, I believe the latest versions of CC (19.1.1) and ACR (10.2.1.895).
It's a bit of a nightmare restoring all your preferences and settings, and one I can't manage to get right means that JPEGs opened with the ACR filter in Photoshop have a distinctly more saturated (redder) tone than the Photoshop image. (I use the ACR filter as a simple, do-everything correction tool for JPEG snaps - my RAW files seem better, but still not identical.)
For the purposes of the jpegs, I have set the colour space to sRGB in PS, although the version of ACR which opens when I use the Filter>ACR option gas no link for ACR settings at the bottom, just "cancel" and "OK" buttons, so no way of seeing what the settings in ACR area.
Obviously I am missing something - it's so long since I have had to alter any of my PS workflow that I'm at a bit of a loss. I'm not that experienced beyond fairly basic PS use, so if you have any idea what IO am doing wrong please try to keep it simple!
I have seen variations on this problem on the forums, but nothing quite the same.
This sounds like a defective monitor profile. Are you on Windows 10 by any chance? It's known to install low quality monitor profiles when doing updates.
Try setting the monitor profile to sRGB. Go to Control panel > Color management, add the sRGB profile, then set it as Default.
Make sure Use my settings for this device is checked. Restart Photoshop for the change to take effect.
If this fixes the problem, you should ideally calibrate your monitor with a hardware calibrator, which will create a profile that accurately describes your monitor.
the version of ACR which opens when I use the Filter>ACR option gas no link for ACR settings at the bottom, just "cancel" and "OK" buttons, so no way of seeing what the settings in ACR area.
ACR and the Camera Raw filter are two different things.
ACR is designed for raw files, and the Workflow options are required because some decisions have to made about how the new, rendered file should be rendered. Like color space, bit depth and dimensions.
The Camera Raw filter is designed for files that have already been rendered (like jpg, tiff, etc), so the Workflow options are not relevant.
IOW, the Camera Raw filter works like any other filter in the Filter menu.