Finding heldback packages

pacman

pacman

 -Si <package> | grep Version    # version in the repo
pacman -Qi <package> | grep Version    # version installed

Or for all ignored packages at once:
pacman -Qu

This lists everything with a newer repo version, and packages in IgnorePkg are still shown, marked with [ignored] at the end of the line. A plain pacman -Syu also prints a warning per ignored package with the old and new version before it lists the rest.

To confirm what you actually froze (and how):
grep -E '^(IgnorePkg|IgnoreGroup)' /etc/pacman.conf

apt package manager

apt-mark showhold                # which packages are on hold
apt list --upgradable              # held ones appear as well, with the new version
apt policy <package>          # Installed vs Candidate version

To release it once you have checked the changelog:
apt-mark unhold <package>

If you want to read the upstream fix first:
apt changelog <package>
shows the candidate’s changelog.