Managing many clients means every List has unique needs. Setting default Custom Field values per List would save time, reduce errors, and keep tasks consistent—making workflows faster and more organized.

This is very needed. Example: there's a field name 'Account' that holds the client to which this task is related. If there is also a List specifically devoted to that Client, tasks created there should have that field pre-populated with the default option.

I know automations can solve this but it requires to create rules for every single operation (create task, move task, edit field...).

Yes for this.