I like using the tool called “import”. It’s a command line program that takes a filename for it to write to. It gives you the option to write whatever save name logic you want around it.

Try flameshot.

I think you can do that with the default app but I don’t use Ubuntu/Gnome and may be wrong. I hope this link may give you a starting point: https://www.tecmint.com/take-or-capture-desktop-screenshots-in-ubuntu-linux/