Is a marriage considered legally valid in the absence of the guardian due to his presence in another country, given that there is documented consent from him and the bride, and the presence of two witnesses? And is his presence required at the same marriage ceremony?

For a marriage contract to be complete, it must be performed by the guardian (wali) or his agent. If the aforementioned document only includes the guardian's approval of the marriage, this is not considered an authorization for the person responsible for marriage contracts. If the agency is not valid, the contract is فساد (fasid - corrupt/invalid), and it must be renewed by having the guardian complete the contract, or by authorizing a specific person to perform it, while fulfilling the conditions for a valid contract.