Some users are experiencing difficulties when attempting to save newly edited texture files using the Luna Paint Image Editor in VSCode. This can be solved by turning on the "Auto Save" feature in VSCode. You can follow this article for more information Luna Paint Image Editor won't save the texture (.PNG) file in VSCode – Codakid. If this doesn't work for you, then you can use the Pinta image editor to edit the texture file.
1) Go to the below link and download the Pinta app according to your OS.
Pinta Link: https://www.pinta-project.com/releases/
2) Open your project in VSCode and locate the texture file you want to edit. Right click on the texture (.png) file and select the "Reveal in File Explorer" option.
It will open your texture file in the file explorer.
3) Drag the texture file to Pinta's window. You can now begin editing your file and save it once finished.