That is of course assuming Putin would actually have tried this if Trump was still in power. IMO if Trump had retained the presidency in 2020 then Putin would have had to postpone his invasion until 2024.
After all he took Crimea and part of Donetsk/Luhansk on Obama's watch then during Trump's reign he basically sat on his hands and did nothing except watch Ukraine build up it's defences, that would have been a much better time to strike however he was scared because one of Trump's first military acts was to humiliate Putin and the Russian military in Syria, after which he learnt not to "**** with crazy" again.
I don't see any specific reason why Putin would have decided to vary based on Biden. Given Trump was about retracting forces he would not be interesting in Putin's invasion. Other than it being an excellent fossil fuel sales opportunity for Trump.
I think Biden is understated, but don't assume not filling twitter with bile and venom is a weakness. Velvet glove, walk softly and carry a big stick. Biden seem more authoritative and it appears China doesn't view his communication as frivolous like Trump..