This is why I wonder why companies are not working on high capacity backups. We have LTO for tape... and that's it. Not even IBM (IIRC) develops their own format anymore.
We desperately need companies to start doing HVD disks and holographic media. Hell, we had Tamarak with holographic media in the 1990s, and many companies doing it. Yes, there are hurdles, but there were hurdles with CDs and DVDs, which were easily solved. This way, we can get something like a 400 CD jukebox, add a HVD drive, and even at 10TB per drive, have a petabyte of data in one rack unit, with an easy way to offsite the media.
Storage isn't a matter of "can't". It is a matter of "won't". Lasers have gotten better since Blu-Ray was developed. We can have many, many more layers. We can do different types of pit depth (deeper/shallower than the 128 nm), different laser wavelengths... many different technologies where we can easily pack a terabyte, if not ten or 100 onto the platter of a CD-sized disk. If someone made a BDXL format that was 5-10 TB, it would do a lot for storage, especially because CD changers are/were a common thing, so it wouldn't be hard to make one into something similar to a tape library.
As for the filesystem? We can directly back up to the read/write device... or we can just use UDF and packet writing. Yes, UDF is a universal filesystem format, pretty much forgotten about, but would easily scale to multi-terabytes. Even something simple as a `tar` command would provide ransomware resistant backups.
Maybe China's leadership might get some sense and kick some research in this direction. They are the only ones thinking past the quarterly numbers these days.