Certbot does not maintain apt releases anymore. Change to installing via pip.

[molytov]

The apt release of certbot isn't supported anymore.
Instead, they recommend installing certbot via snapd, but there is also the option to install via pip.
It's a few more commands, but it will still function the same as before.

sudo apt update
sudo apt install python3 python3-venv libaugeas0
sudo python3 -m venv /opt/certbot/
sudo /opt/certbot/bin/pip install --upgrade pip
sudo /opt/certbot/bin/pip install certbot certbot-nginx
sudo ln -s /opt/certbot/bin/certbot /usr/bin/certbot

The rest of the commands are the same.
https://certbot.eff.org/instructions?ws=nginx&os=pip