I've never screwed up updating a PS4 from 8ish to 9.00, just download the specific FW, then install it via the Safe Mode.
Of course, always turn off the network, delete whatever notifications, and disable automatic updates (that does worry me when initializing a console, though thankfully it just factory resets it).
Sony sure doesn't want people on older firmwares, but those of us who have it we're lucky. And those with PS5s on low firmwares, even luckier (it's hard to find one on a low FW).