This is absolutely the correct information. I sold UPSs for years and the general consensus is that if you want more than 5 to 10 minutes of power, then you want to go with an actual generator solution
Saying that, UPSs tend to be used in industrial environments to keep machinery running until the generator starts up and can accept the load.
Holy shit, I have not heard that name in many years. Definitely a +1 for reminding me of all the fun I used to have in this title
For lighting, I would personally avoid smart bulbs, especially if you are redoing the apartment anyway.
All they lead to from my experience are annoyances when guests/partners inevitably flick a switch and turn off the smart bulb.
I live in Australia so the spec may be different from where you are, but I have found ZigBee to work amazingly.
If you only need it to skip the power outage, I would look at something in the range of 800W to 1000W in an online ups.
This wattage should run your devices for 5 minutes or so, as you have quoted them. The online UPS will always run its load off on the battery, so there is no swap over time. Other types will be fine for a PC or normal electronics, but the hitch in power could cause a defect in the 3D print.