That was an unwritten rule even back in the DOS days. It was healthier for the PC to stay on rather than turn it off every day.
zeugma, I tried to reach the end (to make sure it wasn’t already stated) before I mentioned this, but another possibility is that you may have too much plugged into the UPS.
Also, if you have a laser printer connected, that could be the issue too. Laser printers are a no-no for a UPS because they use a power surge to use the fuser (the thing it melts the toner to the paper).
All the other assistance here on this thread have probably already covered your problem, but I thought I would throw this in too.

Back in the day, many folks did this. But the hardware that suffered was the hard drive. I know because I used to do it and even with drives spinning down and such, I lost a couple after 2-3 years of leaving them running. Makes for a bad day if you don't have a current image handy.
These days with SSDs...not a bad idea for a Linux box. Windoze? Not so much.
zeugma, I tried to reach the end (to make sure it wasn’t already stated) before I mentioned this, but another possibility is that you may have too much plugged into the UPS.
Nope just 2 things. An LCD monitor and the desktop itself.
I moved the Laser printer into another room quite a while back. Don’t know if the 2 rooms are on the same circuit though. Probably ought to check that.Also, if you have a laser printer connected, that could be the issue too. Laser printers are a no-no for a UPS because they use a power surge to use the fuser (the thing it melts the toner to the paper).
Back in the day, if my memory serves me correctly HD failures were the most common computer failures. I retired a couple of years before SSD drives were common and affordable. My aging mac-mini and dell laptop have energy saving settings that spin down the HD when not in use. So far, so good after 10 years and 6 years respectfully.