I’ve worked on these systems. You might as well be asking F1 drivers for tips to help you commute to work.
The hyperscale stuff is not built on top of ordinary filesystems. It’s all clusters of machines, and error correction is handled at the level of clusters. If you’re evaluating systems like ZFS and BTRFS, then you’re already working with a radically different tech stack.
At scale, your file metadata is stored in a distributed database of some kind, and the file contents are stored with forward error correction across multiple machines in a cluster. Or something similar, but stored across multiple clusters. The pricing models for cloud storage are designed around the usage patterns—like, if you know that some data is going to stick around for 90 days, then SMR is a win. If a file could get deleted at any time, then SMR is a loss.