Is a marriage contract by video call or online valid?

This is a contemporary matter of difference; many Shafi'i scholars require the wali, the groom and the witnesses to be physically present in one sitting, so a contract by video is not accepted by most religious affairs offices in Malaysia.
Some contemporary scholars permit it if all parties can be seen and heard live without doubt. The safe solution is for a wali or groom who is far away to appoint a representative who attends in person. During the pandemic, some states granted specific relaxations under guidelines. Always consult your state Islamic Religious Department before planning. See Marriage contract.