Read This for AnimatedGif on Monterey; It works just fine.

[QuantumLibet]

Step-by-step instructions to get AnimateGif working on Monterey:

1. Download AnimatedGif.saver.zip
2. Double-click AnimatedGif.saver.zip to uncompress it to AnimatedGif.saver
3. Double-click AnimatedGif.saver to install it
4. Install it "for this user only"
5. Wait until the System Preferences > Desktop & Screen Saver opens by itself
6. Choose AnimatedGif screen saver
7. Click "Screen Saver Options…"
8. Choose a Gif >> THAT IS IN THE PICTURES FOLDER! << You can change that later.
9. Click on "Preview" when hovering over the preview window
10. Wait for the dialog that "AnimatedGif.saver can't be opened..."
11. Click on "Show in Finder"
12. Wait for the Finder window to open
13. Right-click the AnimatedGif.saver file and choose "Open".
    Nothing happens. This is by design.
14. Change back to the System Preferences > Desktop & Screen Saver dialog
15. Switch to any other screen saver, then back to AnimatedGif
16. Click on "Preview" when hovering over the preview window
17. Wait for the dialog that "AnimatedGif.saver can't be opened..."
18. Click on "Open"
    Now the screen saver chosen starts. And will so in the future, without any dialog.

Why all this?
Unknown binaries are not executed by default without valid (or no) certificate. The "right-click and choose open" is a way to tell macOS that you don't care for validation, and it will remember that choice, once made.