It has an important caveat though: both the USB and 12v outputs are unregulated, so the device you're feeding into must be able to handle a wider voltage range, or you can buy a fairly cheap ($15 or so) step up/down converter to put in-line with it.
I'd really like an affordable 5v/12v UPS though. Maybe it will happen when more things adopt USB-C and there's more of a market for power banks designed for seamless switching.
There are also few simpler ones that do "just" supply power and "power good" signal.
There is also plenty of DC UPSes, although often targeting the industry, which means "expensive"
In-between is [2] OpenUPS but I didn't used it. It's just pretty niche product and niche is also one of the "it will be expensive" keywords.
Soo yeah, they are out there and work fine, go and buy one. Oh, don't want to spend more than rPi ? Well, that's the price of niche products, even if parts are not super expensive it need to cost enough for NRE costs to amortize.
Or, slap a power strip and few power supplies into normal UPS and call it good enough
Some people use power banks for that, but that's not really proper use and some power banks don't allow seamless power switch.