I know how RAID work and prevent data lost from disks failures. I want to know is possible way/how easy to recover data from unfunctioned remaining RAID disks due to RAID controller failure or whole system failure. Can I even simply attach one of the RAID 1 disk to the desktop system and read as simple as USB disk? I know getting data from the other RAID types won’t be that simple but is there a way without building the whole RAID system again. Thanks.
In this case, you need a new RAID controller of similar type.
No. One disk out of a RAID array is different from a normal disk.
Recovery becomes easy if you do not use a hardware RAID controller, but a ZFS software RAID instead. It does nearly all automatically. But you need to do a little more reading tutorials for the first setup.