Could be useful to backup data in bluerays? Or it will rot anyways

You still get rot as CD-R and BD-R both use an organic dye. There were some discs meant for archival (M-Disc) that should hold up for much longer, but folks are finding out brands are now selling regular BD-Rs as M-Disc.

If you want something that won't rot, you need discs that use inorganic dyes, such as the M-disc. Only issue is M-discs require a more powerful laser to burn.