The heat generated in a system is directly proportional to the...

Joule heat is given by the formula $H = I^2 R t$, which means the heat generated is directly proportional to the square of the electric current ($H \propto I^2$).

Peltier heat is given by $H = \pi I t$, which means the heat generated is directly proportional to the electric current ($H \propto I$).

Thomson heat is given by $H = \sigma I \Delta T t$, which means the heat generated is also directly proportional to the electric current ($H \propto I$).

Since the given heat generated is directly proportional to the electric current passing through the system, it can be Peltier heat or Thomson heat, but it cannot be Joule heat.