Grandfather inadmissible to Canada, is there any chance to appeal?

In April of 2022 my grandfather applied for a Canadian visa under the CUAET program and in May of the same year he submitted his fingerprints. After more than two years for waiting for a passport request he got this response from IRCC:

"I am now completing the assessment of your application for a temporary resident visa you submitted on April 02, 2022. It appears that you may not meet the requirements to travel to Canada.

Paragraphs 34(1)(d) of the Immigration and Refugee Protection Act state that a permanent resident or a foreign national is inadmissible on security grounds for

(d) being a danger to the security of Canada;

In your application, you stated that you served with the Strategic Missile/Rocket Forces (RVSN) of the Soviet Union in Kalinkavichy Belarus from May 1981 to June 1983.

The Missile Forces, also known as the Strategic Missile Forces of the Soviet Union (RVSN), were a military branch of the Soviet Army that controlled the Soviet Union's land based intercontinental ballistic missiles (ICBMs). In 1987, the Government of Canada's Department of National Defence indicated that the principal direct threat to Canada at that time continued to be a nuclear attack from the Soviet Union via ICBMs.

Given your military service in a Soviet unit linked to the proliferation of weapons of mass destruction, I have reasonable grounds to believe that you are inadmissible to Canada under paragraph 34(1)(d) for having engaged in an activity constituting a danger to the security of Canada."

Firstly, it seems kinda harsh. In USSR the military service was mandatory for all males. He was a conscript, not a volunteer, and also didn't get to choose where to serve and at what position. And secondly, what took IRCC so long to reply? He provided all of the required information during the initial application.

So, is there even a small chance to somehow appeal this decision? And if yes, would that be, as initially planned, on CUAET terms, or would he need to follow the general immigration procedure?