Just do whatever Pixabay/(any assest license) say. If it says the content is free for both personal and commercial use, then thereās no need to include the artistās name in the credits. But if it says itās only free for personal use and requires credit in your game, then you have to credit the artist.
As stated before, the Godot software is licensed under the MIT license. This is a relative free license, you could sell Godot if you want. You could start your own game engine based on the Godot source code.
I have had some heated discussion here on the forum, but there is a second license, for the Godot icon.svg, that is added to every new project, that has itās own license. If you display the Logo at game start you have to credit Andrea Calabró (CC BY 4.0 International)
Default the Godot logo is shown, you can switch it off and replace the icon.svg with your own in your game.
Nearly in all Open Source projects there is a distinction in the licenses for source code and artwork (In Godot MIT and CC BY)..
In your game you are not forced to any of these licenses to do the same for your game. You are free to do with your game, developed in Godot, whatever you want. If you donāt add your own license to your game, all rights are reserved to you.
For the assets by Pixabay, they are relatively open, there is no need to credit the artist, but it is welcomed to do so. You canāt sell the assets as a standalone, thatās all. There are some limits how āadultā or āillegalā your content can be, where you are allowed to use the assets. https://pixabay.com/service/license-summary/
So far with your decisions, there is no limit how you can release your game, it could be closed source with no attribution to anyone (exception the godot icon), or fully open source.
Iām not a lawyer, this is no professional advice!