How do I make the crop guidelines more visible (increase thickness and/or change color)? As they are right now, I can barely see them making them almost useless. Question applies to Lightroom Classic CC as well.
There is no such setting within Photoshop or Lightroom that changes the thickness of crop guidelines or changes its color.
However this issue has been reported in our Feedback community Lightroom Classic: Overlay is very hard to see (Crop/Transform) | Photoshop Family Customer Community and our Engineers are working on it. Be sure to click the Me too button in the upper-right corner.
One thing that came out is if you uncheck the option "use graphics processor" in both Lightroom and Photoshop it might have some considerable difference to the guideline visibility.
Let us know if the above suggestion helps.