There is a error with the FS-UAE GPG keyfile. To update, go to the command shell and run the following commands. Then re-run the apt command.

(All one command)
curl -fsSL https://download.opensuse.org/repositories/home:FrodeSolheim:stable/Debian_12/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_FrodeSolheim_stable.gpg > /dev/null

sudo apt update