Maybe it is not the best way to solve a problem, but perhaps different opinions may give me some ideas.
At the moment, I have three pc's and a windows tablet, all running w10, the majority r1809, on my network. They are backed up automatically each day by a hp server, running windows server 12 R2. However the latest w10 (1903) does not connect with the server, but can access files there. At the moment, w10(1903) is only on one pc, that does not need backing up much, it only has a few programs and the operating system, but the laptop and desktop pc will be updated sometime soon to 1903. Microsoft are not supporting the server software, anymore, afaik, wanting users to update to server 19. The advantage of the server is that it just works, (within the limits of hp hardware and MS software) and the 8 mirrored sata drives are written in ntfs format, so can be read, if server fails, by another windows pc.
Many years ago, I used 'sync back pro', from 2bright sparks, backing up files to other pc's, and I'm thinking about doing that again. I could sort of software mirror files to two independent usb drives. That gives most options for recovery, if one drive fails, I can read the other via one of my other pcs. I was thinking of using Nas, but afaik, they use proprietary formats, e.g. not purely ntfs, and if the unit fails, then I have to either get it repaired, or have another identical unit to get at the data files. I believe usb 3 is quite fast enough for what I need, but as my desktop pc does not have usb3, it seems most likely to get a separate pc, just as a file server. Intel do them (nuc) and others, with numerous usb ports, and not much else.
At the moment, I've about 12Tbytes stored, not doing much streaming, no games so speed not too critical. I suppose none of the data is important, my world will not end if it all is lost, but hdd storage is cheap compared to thinking 'if only I'd kept that'.
So, any other ideas? I've not completely decided, but I'll have to fairly soon.