Kopia supports zstd compression, I found it to be within +10% to -5% of the size of my Borg repo.
It also has extensive support for ignoring stuff and it works very well.
I still use Borg because its policy of expiring older snapshots is more useful for me, but Kopia is extremely solid and I would use it any day if I didn't care that it doesn't actually keep one monthly backup for the last 3 months as Borg does (it decides which older snapshots to keep with another algorithm; it's documented on their website).
It also has extensive support for ignoring stuff and it works very well.
I still use Borg because its policy of expiring older snapshots is more useful for me, but Kopia is extremely solid and I would use it any day if I didn't care that it doesn't actually keep one monthly backup for the last 3 months as Borg does (it decides which older snapshots to keep with another algorithm; it's documented on their website).