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Use an associative array to store the certificate names per role and environment.

#! /bin/bash

unset -v envs
declare -A envs

while IFS='| ' read -r certname role env; do
    envs["$role.$env"]+="$certname"$'\n' 
done < /tmp/inventory.list

for e in "${!envs[@]}" ; do
    printf '%s\n' "[$e]" "${envs[$e]}"
done

To sort the sections, you can print the keys, sort them, and then read them back and output the associated values:

for e in "${!envs[@]}" ; do
    echo "$e"
done | sort | while read -r e ; do
    echo "[$e]"
    echo "${envs[$e]}"
done

Use an associative array to store the certificate names per role and environment.

#! /bin/bash

unset -v envs
declare -A envs

while IFS='| ' read -r certname role env; do
    envs["$role.$env"]+="$certname"$'\n' 
done < /tmp/inventory.list

for e in "${!envs[@]}" ; do
    printf '%s\n' "[$e]" "${envs[$e]}"
done

To sort the sections, you can print the keys, sort them, and then read them back and output the associated values:

for e in "${!envs[@]}" ; do
    printf '%s\n' "$e"
done | sort | while read -r e ; do
    printf '%s\n' "[$e]" "${envs[$e]}"
done

Use an associative array to store the certificate names per role and environment.

#! /bin/bash

unset -v envs
declare -A envs

while IFS='| ' read -r certname role env; do
    envs["$role.$env"]+="$certname"$'\n' 
done < /tmp/inventory.list

for e in "${!envs[@]}" ; do
    printf '%s\n' "[$e]" "${envs[$e]}"
done

Use an associative array to store the certificate names per role and environment.

#! /bin/bash

unset -v envs
declare -A envs

while IFS='| ' read -r certname role env; do
    envs["$role.$env"]+="$certname"$'\n' 
done < /tmp/inventory.list

for e in "${!envs[@]}" ; do
    printf '%s\n' "[$e]" "${envs[$e]}"
done

To sort the sections, you can print the keys, sort them, and then read them back and output the associated values:

for e in "${!envs[@]}" ; do
    echo "$e"
done | sort | while read -r e ; do
    echo "[$e]"
    echo "${envs[$e]}"
done

Use an associative array to store the certificate anmes per role and environment.

#! /bin/bash

declare -A envs

while IFS='| ' read -r certname role env; do
    envs["$role.$env"]+="$certname"$'\n' 
done < /tmp/inventory.list

for e in "${!envs[@]}" ; do
    echo "[$e]"
    echo "${envs[$e]}"
done

Use an associative array to store the certificate names per role and environment.

#! /bin/bash 

unset -v envs
declare -A envs

while IFS='| ' read -r certname role env; do
    envs["$role.$env"]+="$certname"$'\n' 
done < /tmp/inventory.list

for e in "${!envs[@]}" ; do
    printf '%s\n' "[$e]" "${envs[$e]}"
done