from those two posts:
1. How do I put a png over a gif I have without it changing?
2. Put your transparent (alpha channel) png layer at the bottom of the stack and then Filters > Animation > Overlay background
The essentials
A gif is a color indexed image and the png probably (but not always) RGB Change the gif to RGB: Image -> Mode -> RGB before anything else.
EDIT: Forgot this bit of advice. If the gif is "optimised" (sometimes looks like bits of layers missing) then use Filters -> Animation -> Unoptimise and Gimp creates a new set of complete layers
Filters > Animation > Overlay background comes from a third party script. sg-combine-bg.scm It adds two entries combine background and overlay background. It has been posted before, but once more, download attached, unzip put the .scm in your Gimp users scripts folder.
Before exporting as a new gif or webp remember to remove the bottom layer you added.
1. How do I put a png over a gif I have without it changing?
2. Put your transparent (alpha channel) png layer at the bottom of the stack and then Filters > Animation > Overlay background
The essentials
A gif is a color indexed image and the png probably (but not always) RGB Change the gif to RGB: Image -> Mode -> RGB before anything else.
EDIT: Forgot this bit of advice. If the gif is "optimised" (sometimes looks like bits of layers missing) then use Filters -> Animation -> Unoptimise and Gimp creates a new set of complete layers
Filters > Animation > Overlay background comes from a third party script. sg-combine-bg.scm It adds two entries combine background and overlay background. It has been posted before, but once more, download attached, unzip put the .scm in your Gimp users scripts folder.
Before exporting as a new gif or webp remember to remove the bottom layer you added.