South Carolina has long had a requirement for mail-in absentee ballots that the ballot envelope be signed by the voter and by a witness.
For the June primary, a federal judge struck down the witness requirement on the grounds that during the pandemic emergency, the requirement would place some voters in danger. The state election commission and the LWVSC advocated that the recent legislation allowing no-excuse absentee voting also remove the witness requirement for the November general election, but the legislature did not include that provision.
A lawsuit was filed in the same court and the same judge removed the requirement. On appeal, a three-judge panel reinstated the requirement, then the full appeals court reversed the panel decision. The appeals continued to the Supreme Court, which ruled that the requirement could stand while the lower-court proceedings continued. That ended the matter, at least through the election.
So where we stand now is, you need to get a witness signature. The witness needs to sign and provide an address. Anybody who can sign their name and write their address can be a witness. There is no age limit, no requirement that the witness be a voter, no need for a notary. Just make sure someone signs.