the exclusion is relative to the root of the source.
--exclude "/testFolder/t1/"
https://rclone.org/filtering/#patterns
" If the pattern starts with a / then it only matches at the top level of the directory tree, relative to the root of the remote"
you posted your rclone command as rclone copy "SourceteamDriveName:testFolder" "DestTeamDrive:testFolder" --exclude "SourceteamDriveName:testFolder/t1"
and now you have changed it to something else.
what command are you using?
what is the structure of the remote?
what are you trying to exclude?
in the second example, if you are trying to exclude the t1 folder, --exclude /t1/