How to install a specific version of freeradius via apt?

[Mark Antony]

Based on Freeradius website, it is possible to

echo "deb https://packages.networkradius.com/releases/debian-buster buster main" >> /etc/apt/sources.list
sudo apt-key adv --keyserver keys.gnupg.net --recv-key 0x41382202
apt update

But it doesn't allow me to install the older version 3.0.20:
apt install --only-upgrade freeradius=3.0.20

Is there a way to achieve that?
Many Thanks,
Mark