We've been using Creative Cloud for some time now mainly Adobe Acrobat for PDFs unfortunately lately our highlighting capabilities no longer exist. The button appears and I can click on it but it does nothing. Tried on multiple computers and the same thing happens. Has there been an update that would cause this to fail? We've used a variety of PDFs and its the same on all of them.
To check whether an update might have caused this issue or not, would you mind confirming the exact version of Adobe Acrobat you are working with?
Also, when using the Comment tool for highlighting, is it just the Highlight function that doesn't work or other Commenting tools as well?
For better understanding of this behavior, can you share the screen recording of exact steps performed?
Note: Make sure you have the correct Color selected for the highlighting. For e.g it shouldn't be white, else nothing would appear. You can check it by right click on highlighted text>Properties>Appearance