Try the two settings shown below.

1. When logic synthesis is performed for registered design files, configuration with the minimum resources is given top priority.
Assignments => Settings => Select Analysis & Synthesis from the Category column on the left side of the screen
Set Optimization Technique to Area

2. When placing and routing, the highest priority should be given to constructing with minimal resources.
Assignments => Settings => Select Fitter Settings from the Category column on the left side of the screen
Set More Settings => Auto Packed Registers to minimize area

If you want further minimization, select Tools ⇒ Advisors ⇒ Resource Optimization Advisor and try setting the corresponding items.


* The settings introduced here may affect performance.
Be sure to check that there are no problems with timing verification.