I signed a contract with a venue for a 150 person wedding. Due to COVID, that is now impossible and illegal in the state of California. Being that the venue cannot guarantee that we could proceed with a 150 person wedding, can that contract be void?
This will depend on the exact provisions of the contract. If the contract does not specify what happens if factors beyond the parties' control prevent the fulfillment of the contract, the deal will be undone to the extent possible -- that is the vendor will be released from obligations but will have to return any payments. However, if the vendor has incurred good-faith expenses, it may be entitled to payment for them.
If the contrast specifies what happens in such an event, its provisions will be followed unless they contradict law or public policy.