The drone sightings is a mix of Russian ops, and copycat actors. The jets that violate airspace, are probably a mix of intentional close flying, under the plausible deniability that navigation jamming in the area causes them to cross into neighboring airspace.
In the case of Russian aggression, it is to create more tension. Why on earth would Russia want to escalate this, you might ask? Well, now that pretty much every country west of their border is a NATO member, a Russian attack on NATO would likely trigger article 5.
If Russia can provoke any NATO countries to attack first by, say, downing some airplane of theirs (fighter jets, recon, strategic bombers, etc.), they can use this as casus belli, and use it as propaganda. One thing Russia learned after 2022 was that any larger scale mobilization is incredibly unpopular. They can't mobilize millions of soldiers without any real cause, and march into the west. If they can sell the idea (with "proof") that NATO is actively attacking Russia, that's another thing.
They're probably also banking on the fact that the heightened situation will scare people in the west, which in turn will make them vote for isolationist parties that don't want to commit. One thing is to talk about war, another thing is to actually see the writings on the wall.
I don't think European NATO members can do much other than to just keep reinforcing and fortifying their borders, build up their armed forces as if Russia will invade tomorrow, and dig in. And keep hammering Russia with sanctions.
The imperialist dreams of Russia is the expand into the ex-Soviet countries. They've tried election meddling, which worked to some degree, but I think they know that to achieve their goals, they need some larger conflict to happen - so that they can annex the desired areas when peace talks come up.