Hello, i have macbook pro 14inch, brought it weeks ago. i have a big issue it is turning off by itself, when battery is 20 percent. what can i do

See if there is info here that helps: Get help with your Mac notebook battery - Apple Support

...brought it weeks ago

Then it is under Apple's standard warranty. Please contact Apple about evaluation and if needed, service.

Try a SMC reset: How to reset the SMC of your Mac - Apple Support

If you have a Mac with Apple silicon, make sure your computer is plugged into external power, then just

restart your computer. You can skip the rest of the steps in the above linked to article. 

Leave it plugged in so that the battery does not drain to 20%.

You are putting undue stress on your MacBook Pro battery, dooming the battery to a much reduced life overall. Typically, MacBooks will shut down to protect the battery when it gets to a point where under use it could be harmful to continue running. Chances are if you have your MBP checked by Apple, they won't find anything wrong with it.

To avoid this, if you are going to continue to use your MacBook in situations where you can't charge the battery or use it plugged in, buy yourself an external battery bank, keep it charged and have it with you, so you don't continue to run the battery down, shortening its useful life.

deafrombaden-würtenberg wrote:

thanks, but that's not a solution unfortunately

Why is that not a solution? You said it turns off when the battery drains down to 20%. It won't turn off if the battery remains charged. I guess I am not understanding your issue. Is there something else that you have not told us? What exactly is the problem? Do you not want it to turn off when the battery drains?