Actually the timing makes sense. I'm guessing they have been asking to fight the war more on their terms but we've been holding them back. I'm guessing you think Biden woke up this morning and was like screw it, let er rip, but the more likely scenario is our intelligence community somehow figured out Putin is counting the days until Trump gets in office and doesn't want to do anything stupid before then.
Based on your assertion that Biden is practically a vegetable, if it wasn't his decision then it was someone high up in the DOD who knows how to handle things. If you are incorrect and Biden is, well just an old guy who happens to still be the President, then he relied on intelligence from someone high up in the DOD and made a calculated decision. Either way it wasn't a spur of the moment call.
Now, if you want to go full conspiracy theory, it could be an attempt to get us sucked in more right before Trump gets into office just to screw with him and make him look bad if we stand down when Russia escalates but I don't believe that is likely. If that were the case we would have provoked them enough to escalate the conflict earlier in the year and the dems would have attempted to find a way to make Harris look like some sort of capable wartime leader. I say attempted because nothing else they tried in the run up to the election worked so I doubt this would have as well.