I have an electric power strip managed on Android with Smart Life.
With this I turn my PCs on and off even when I’m not at home.
However, I don’t like that the Smart Life server is abroad, probably in China.
I would therefore like to replace it with Home Asisstant and I see that I can install it on TrueNAS SCALE and obviously on Android.
The problem is that the NAS is also connected to the electric power strip and if it is off the app on the NAS is obviously not active.
I wonder if with the app on Android I can still turn it on by controlling the electric power strip.
SmartLife relies on an external server, but I noticed that sometimes it works even when the Internet connection is absent.
Maybe even with Home Assistant there is no need to always have the server active, but I have never used Home Assistant.
Can you give me some advice?
Hello Welcome to the HA World, you my friend have a long way to go! 
The idea of Home Assistant is that it should run 24/7. Some people use a Raspberry pi for it, I like to use a MiniPC, having this, will convert Home assistant into the replacement of that “server on china” (when possible!).
There are some Tuya/SmartLife that can be controlled by HA without the need to talk to the server (see GitHub - make-all/tuya-local: Local support for Tuya devices in Home Assistant and GitHub - rospogrigio/localtuya: local handling for Tuya devices)
As a piece of advice, Tuya is a cloud based company, they try to do all the possible to get you to depend on their cloud service (IHMO).
When I started I had some WiFi tuya/smartlife devices and now I have throw almost all of them away and replace them by local ones (like Zigbee or wifi with ESPHome or Tasmota devices).
Cheers!
If it runs with a compatible MCU you can probably free it (ditch the cloud firmware) and install esphome on it which also allows direct control via webserver 
If it is really smart to put your (ha) server on a switch is another topic 