The finny thing is that , THAT is my backup drive, mostly. It has lots of crap, including GB synced from Google Drive (photos being the mos important). Other than that, it's stuff I could re-download from elsewhere, but 3TB is a lot to re-download. Aah yeah and it also has the TimeHift backups.
I thought of going EXT4 , but as you said, NTFS is more widely supported.
I also used to run btrfs in btrfs-RAID10 configuration until apparently a flapping SATA link and fsck attempts were able to break the fs completely. Full system backups were great that day. I run https://kopia.io/ nowadays every three hours during day time and I've been quite happy with it.
Nowadays I run bcachefs.. Backups are still handy :).
I suppose the reason why you chose NTFS was to be able to access the data from Windows, at least in case of emergency? Because there are a lot of filesystems that are presumably more mature than NTFS is for Linux.