Being able to connect to a second screen with my ZFold 7

[Quarryheath]

I would like to be able to use second screen with my Fold 7.

Ideally use a tab A9 but if not a tab S7 as the second screen

[CEParsons]

DeX is available on Fold 7. You can use a monitor as a secondary display with a desktop-like interface via USB C > HDMI.

To my knowledge, there is currently no way to use a galaxy tablet as an external display for a galaxy phone.

Multi Control is likely the best solution for what you're trying to accomplish.