Hi. I just bought a 20 amp portable induction cooktop to brew beer in the basement. Is it possible to plug this into a 30 amp adapter with a 4-prong plug and plug this into my dryer outlet?

20A and 30A mean nothing without knowing the voltage. The dryer is a 120/240V circuit, but if it's older it's likely only a 3-wire (non-grounding) circuit.
What is the voltage on the cooktop?

FYI, there is no such thing as a factory made adapter for this.