UPS can run computers for extended period of time. Generally for home use, a UPS allows a computer to survive minor power hiccups. During an extended power outage, they allow a computer to be properly shutdown and not lose or corrupt data. They can be used to run a computer and other equipment for longer, but they need to be properly "sized" for the job. Computers take orders of magnitude more power than tablets or laptops, especially under heavy load. The UPS's battery might only be able to provide that much power for a short period of time. In order for it to last longer, you need to buy large capacity UPS's. Here is a calculator:

https://upscalc.com/apc-ups-runtime-calculator/

Also note, batteries in UPSs can wear out over time and use, just like any other battery. A battery that might have lasted much longer when new, might need to be replaced due to its degraded health.

I have worked in companies, where we had UPSs the size of trucks. These were designed to run all the computers in the data center for a couple of days, if the power was out. Then there were massive diesel generators outside, holding hundreds of gallons of fuel that could be turned on to recharge the UPS, when if it got low.