Left click not working after sleep -- Answered
Same as the thread at Left click not working after sleep which was stupidly closed (thanks Apple Support).
Wanted to re-open because I fixed my issue. In my case, IMac wouldn't allow left click after coming back from sleep but everything else was fine. It turns out that I had another mouse on the bluetooth which had accidentally been turned on. So double check your other mice or bluetooth connections for interference and it may just solve your issue.
iMac with Retina 5K display