I just put my image archive for the last 20 years on a single 100 GB BDXL disc, around 11 000 files. Granted these are mostly cell phone photos, not RAW or anything like that. I did the same with documents on an M-Disc DVD and email mbox-archive on another M-Disc DVD. All disks with copies of dvdisaster and a separate slimline usb-c drive. Chucked offsite in a fire proof safe. I think M-Discs or any HTL bluray a fine supplement to an otherwise comprehensive backup strategy.