Workflow approval template not available

Trevor - I solved this issue for us last week.  I had read a number posts that said to de-activate and then to  re-activate the workflows.  This did not work for me.  The solution that did was to open Designer and rename the wfpub folder to wfpub-old.  Then we deactivated/reactivated and Designer made a new wfpub folder and the templates became available for use.  I think something must have gone wrong in the initial creation of the site collection and the wfpub files had something wrong with them. I'd be curious to see if this fixes your issue also.

You might also take a look at this if you haven't seen it: https://docs.microsoft.com/en-us/sharepoint/allow-or-prevent-custom-script.  It is what MS support told us to do, but we had already done the folder fix.