For what it’s worth, there’s an FSF article that addresses this:

https://www.gnu.org/philosophy/programs-must-not-limit-freedom-to-run.html

Whether it’s persuasive is of course up to you to decide ;).

I’m using Borg and it’s fine at that scale. I don’t know if it would still be viable with 100TB or whatever. The initial backup will be kind of slow but it encrypts everything, and deduplicates it too if I’m not mistaken. In any case, it deduplicates the common situation where you back up another snapshot later. Only the differences get written in the second backup. So you can save new snapshots fairly quickly and without much additional space.