I found out I can highlight pdfs with okular in-file by the review tool, but everytime I use the highlighter, it gets turned off afterwards again, so to highlight the next piece of text I have to activate it again.
I would like to change this behaviour to 'toggle' on off by clicking (or pressing 4), and not have it turn off automatically.
I saw here that the tools can be modified, but it doesn't mention toggling.
Double-clicking the tool solves it, as I found in a Bug report pointing to the manual.