iOS 15.2. Issue still persist. This is some basic level functionality that is not working. How to reproduce the bug:
Open safari.
Search for anything in Google.
Navigate to a gif in images search results.
Wait for gif to fully load.
Long press on gif.
Tap on «Save to photos» button.
Open photos app.
Realize that you have a single frame of animation.
Solutions:
Save as many frames as your GIF have. Using third party software compile a video from these frames. Save results as a gif or mp4.
Record your screen to have HD version of your GIF.