Installing on Ubuntu 21.04

using the new procedure replacing apt-key.......Ubuntu 21.04 now requires a valid port number to linuxcnc.org repository in order to automatically get the key. So knowing that the key is 3cb9fd148f374fef doesn't help me at all
Looks like Ubuntu has tightened security over Debian which uses the old ppa method apt-key method

GlasairMan wrote:

Looks like Ubuntu has tightened security over Debian which uses the old ppa method apt-key method

Not according to this:
www.linuxuprising.com/2021/01/apt-key-is...ated-how-to-add.html

GlasairMan wrote:

I tried to install the ppa keyring
sudo apt-key adv --keyserver hkp://keys.gnupg.net --recv-key 3cb9fd148f374fef
but it was rejected as apt-key now deprecated

forum.linuxcnc.org/9-installing-linuxcnc...nd-easy-installation
There are 3 more keyservers there thanks to PhillC.