You need to use range_year (or range_month, etc.) in order to have sequences.

The setup for this is:

1. Tick the box: Use subsequences per date_range
2. Enter periods and a starting number (optional if using year)
3. Use range_year or range_month (etc.) in the prefix

If you don’t create a date range, Odoo will automatically create one for the calendar year (as per the above example), but you will have to create the monthly, weekly, and other ranges manually.

https://odootricks.tips/sequence-document-numbering