I’ve used Backblaze for a few years and generally no complaints (via Win OS).
My only issue is that it doesn’t back up ISO, EXE and MSI’s, I can understand why, but I wonder if there’s a workaround? So far I just mirror it onto another hard drive, as well as one off-site.
I use them as well for backing up my NAS and I encrypt whatever gets uploaded before, which of course allows me to store whatever I want there.
I’d suggest you do the same if you find a client which allows you to do so.