In Germany, the 2003 Invasion of Iraq was widely seen as illegimate and criminal act, and in many aspects as similar to Russia's 2021 escalation of its invasion of Ukraine. German news unambigously revealed the US governments claims about WMDs in Iraw as lies. There were bigger protests on the streets than ever before. There was some opposition to Gerhard Schroeder's stance on the upcoming Iraq war from the conserative party, but this was less about the invasion being legitimate, but more about the US being a valued ally and "leader of the free world", who deserved some support even when doing wrong.
However, there was a widespread feeling of being powerless compared to the US. Putting economic sanctions on the US was not even discussed, because it was clear that they'd hurt Germany much more than the US. Even more so, Germany was not used to any kind of international leadership role, and many Germans felt doubtful whether Germany could be trusted with power if it had any. Still, this experience kick-started a push for the EU to take a role as a world power in its own right, so that it could eventually stand up to the US if necessary.
There are two more important differences: In 2003, Iraq was led by a rather despicable dictator. Once the US started the war, the best outcome clearly was to remove him from power and then get some kind of democratic government in place. So essentially, before the invasion noone was dieing yet, whereas afterwards it was too late to go back. In Ukraine on the other hand, a complete withdrawel of Russian troops is the desired outcome, hence continued action makes sense.
The last important aspect is that the US is a democracy with a somewhat functioning opposition. Eventually, the American voters got rid of GW Bush on their own accord; and there is probably no way that the European nations could have hastened that. It is worth pointing out that Obama was awarded the Nobel Peace Price for NOT being GWB.