QB Issue Resolution:

no you are not wrong

there is NO line item discount in QBO, never has been

if you use an item for a line item discount, the only way it works is to enter a -1 in the qty, calculate the discount outside of QB and enter it in the amount block

there is also no sub total item, or other charge item used as a percent in QBO

Resolution for Issue 'Discount Rate for per line discounts does not work!' available: Yes (Solved).
Source: Intuit Community forum.

Discount Rate for per line discounts does not work!: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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