Wait, what?!
That's right -- highlighting, the way you have wanted, IS possible in PowerPoint!
(Microsoft 365 & PowerPoint 2016)
As long as your colleagues have Powerpoint 2016 or Microsoft 365, they will be able to view your highlights; they do not need Highlight+ to view the block or text highlights you have created using Highlight+.
They will, however, not be able to edit existing block highlights without a valid installation. If they are running PowerPoint 2016, they will not be able to edit text highlights, either.
If you are using at least PowerPoint 2016, Highlight+ should work -- I have not had opportunity to test in anything other than PowerPoint 2016 or Microsoft 365.
Regardless of your version of PowerPoint, I recommend you try it out, first.