These seem to be the most up to date numbers.
"Rejected absentee/mail-in ballots as a percentage of total absentee/mail-in ballots returned, 2016-2020"
Georgia 2016 6.42%
Georgia 2020 .60%
Source https://ballotpedia.org/Election_results,_2020:_Analysis_of_...
Which cites the official Georgia election website as source of the raw data.