So my 713 Goodtasks (I use it like Evernote and save URLs and To Read lists etc) weren't syncing between my devices (iPhone 7 iOS 13.2, iPad iOS 13.1.3 and iMac 2010 OS 10.13 High Sierra) so I opened Reminders as recommended and that seemed to help. Then today, I got this on my iMac:
The help topics says:
I'm just confirming that the Goodtask app on the iMac is never going to work again because I'm not going to be able to upgrade to OS 13 until I can afford a new computer?
Edited to add: This is what Goodtask looks like on my phone: