Currently MongoDB 7 doesn't support Debian 12, officially.
But we can install MongoDB for Ubuntu 22 on Debian 12.
Following the installation instructions for Ubuntu 22
curl -fsSL https://pgp.mongodb.com/server-7.0.asc | \
sudo gpg -o /usr/share/keyrings/mongodb-server-7.0.gpg \
--dearmor
echo "deb [ arch=amd64,arm64 signed-by=/usr/share/keyrings/mongodb-server-7.0.gpg ] https://repo.mongodb.org/apt/ubuntu jammy/mongodb-org/7.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-7.0.list
sudo apt-get update
sudo apt-get install -y mongodb-org