This represents the disconnect between the East and West.
Trump was despised and not respected in the West where polite norms and pleasantries have reigned during our relative peace and prosperity.
Trump was feared and begrudgingly respected in the East where power, resolve, and a bit of unpredictability are hallmarks of autocratic rule.
Putin was quite hopeful that Trump would continue to drive a wedge between the US/UK and Germany/France in NATO. I would imagine Putin gave a non-zero possibility of Trump actually pulling out of NATO (especially in a second term). That would be a massive win for Putin. That possibility, combined with his unpredictability and willingness to go after other superpowers (look at the trade war with China and strikes on Russian-controlled area of Syria, destroying the Wagner Group in Syria, assassination of General Soleimani), gave Putin pause to pursue more action on Ukraine.
Putin looked at the West's inaction after his invasion of Georgia and Crimea, the disjoined nature of NATO, and Biden's embarrassing withdraw from Afghanistan and saw weakness. He miscalculated that the past actions were indicative of future actions. This, in combination with believing his own BS about Ukrainians wanting to be a part of Russia (although I wonder how much of his own intel community inadvertently contributed to his false perception), set him up for this strategic failure.
The West being perceived as weak and divided represents the greatest risk of WWIII. You have to get out of your American bubble. The world outside of the West doesn't run on pleasantries, social media hashtags, or strongly worded diplomatic statements.
