If I want to add some ducts, will they be Flexi ducts or do they still make Rigid ducts? My old ones are rigid?

I have one duct that connects to three supply vents. The front foyer, the dining room and the laundry room. Air is being split three ways using one duct.

The dining room has the thermostat and one return/one supply.

I need MORE airflow into the dining room so that the thermostat drops easier without me having to point floor fans at the thermostat just to lower it or without the system running endlessly without shutting itself off. I want to run one dedicated independent duct from the dining room supply to the plenum.

The return is near the ground and I feel the cool air is being sucked out of the room before it can reach the height of the thermostat which is 5 feet off the ground versus the return which is 6 inches of the ground.

Let the laundry room and foyer vents run off one shared duct. 50/50.

Dining room one duct, to increase airflow?

Do HVAC people still install rigid ducts or only flexi ducts?

Differences between rigid and flexi?