Cross platform local backup solution

so my current backup system is just rsync and a ext4 partition on a decent disk i keep deactivated when not in use, but im due an upgrade in disk capacity and i figured id like to set up something that will run on both windows and GNU/Linux while im at it, and ideally id like something that can easily be automated.

ive considered just making an ntfs partition, but it seems windows doesnt recognise changes made to it by the linux ntfs software in certain circumstances. id ideally like it to be encrypted with something nice and strong, but obviously i need to be able to make read and write access to it on both GNU/Linux and on windows. a dedicated box is sadly out of the question at the moment, i dont have enough money to pull that off properly unless i can source a dirt cheap power efficient machine with a lot of SATA ports.

as an aside, if anyone has any recommendations for what disks to buy id love them, im looking to pick up a couple of reliable 2+ TB drives with a high MTBF at a decent price, disk throughput isnt all that big of a deal to me as long as its from the last couple of years.