Where to find time & date of previous or last upgrade?

Hello, for my personal fedora log i want to keep track of major changes of my system or apps. I just recently, a few months ago, upgraded from fedora 37 to 38. I wonder if there is a way to find out the exact date of my last (or even all) upgrade? Is the first entry of ‘journalctl --list-boots’ just the first start after the major upgrade? Would be a starting point.

I am thankful for any other approach to track down major fedora upgrades on my system.

# Search DNF history for system-upgrade
sudo dnf history list | grep -e system-upgrade

# Sort DNF history by the number of changes
sudo dnf history list | sort -n -t "|" -k 5