This is exactly what sync-to is designed to do. The repo you setup in Kopia is your “main” repo and sync-to then copies all files from your main repo to whatever secondary repos you want. You can use sync-to with as many secondary repos that you want. Using --delete ensures all secondary repos stay 100% in sync with your main repo. If you don’t use --delete then secondary repos will retain blobs that the main repo has deleted already.
If you use KopiaUI, see https://kopia.discourse.group/t/how-to-automatically-sync-snapshots-to-multiple-repositories-with-kopiaui/