The current version of GoodTask (and v5.3 and 5.2, maybe earlier) appear to have a problem with iCloud Sync--at least for me. When I go to Settings --> iCloud Sync, it shoes that "Automatic Preferences Sync" is enabled and shows a last synced date/time of last night. If I manually click "Upload", the date/time updates to show the current date/time.
If I go to "Backup" down below and click "Upload to iCloud", it shows my preferences as saved along with the current date/time. But then when I go back and then return to the Backup screen, the most recent Backup disappears and it shows my previous backups (beginning with October 29, 2019 and earlier).