Is it possible to execute 2 jobs at the same time with using Arduino UNO?

Just a simple question. Is it possible to do something at the same time with Uno or NodeMCU or Wemos Mini? For example if i have a led and i want to have a fade animation on it when power plugged. And i want to connect the wifi while it's fading.

You can't do two things like this at the same exact time. However, you can do two things so close together that it's indistinguishable to a human from "at the same time".

In order to accomplish this, it's essential that your code is not blocking. Spend some time studying File > Examples > 02.Digital > BlinkWithoutDelay to understand how to write non-blocking code. Compare that code to the blocking File > Examples > 01.Basics > Blink. The delay() statements in the Blink sketch make it so that nothing else can be done during those delays. The microcontroller is running, but it's just stuck in that delay for a whole second. The Uno is running at 16 MHz so it could do many things in that second if it wasn't being blocked.

You can give the illusion of it doing multiple things at once by splitting tasks associated with each process into very short segments. You execute a little bit of one thing, then a little bit of another, then a little bit of the first and so on.

Some libraries may not be very friendly to this style of coding. They might use functions that block waiting for something to happen, for example. The code you write, however, can almost always be done in a way that is friendly to multi-tasking.

It requires a bit of forethought in designing the code.