Have you been using the new make.powerapps interface for your D365 Solution design? Have you been switching back and forth to classic still? Was one of the reasons to activate a process?
Well if your answer was yes, switch no more! From within a solution, if you highlight a process (in this case a work flow) then you will see the Turn On button in the navigation bar.
You will also see it if you click on the 3 dots
A few limitations I have come across so far is that although I can turn on and activate my workflow, if i try and turn off I do get a little error so I have to click into the process and do it that way.
With every week there seems to be a new feature to powerapps that makes customising D365 a little sleeker and I continue to look forward to the next items they release and I hope there will be a few less switches to be needed. I am greatly looking forward to a new interface for workflows so I hope they are on the agenda:)