As mentioned the 4TB Barracuda is an SMR drive. These are pretty useless for RAID as their write speeds are abysmal. In case a resilver is needed it'd take like 10 times longer than with CMR drives, completely defeating the point of RAID. See https://www.servethehome.com/wd-red-smr-vs-cmr-tested-avoid-red-smr/
At least ZFS allows increasing the size of the drives within a mirror pool. Not sure about other RAID setups but it's a pretty easy feature to support so I would expect virtually everything to have it.