Been ratified by all NATO members so I would say that technically they are in NATO
You have to remember that they have been allied partners of NATO for a fair few years as well, so the only change I suspect is that you will see Finnish troops, ships and aircraft in NATO battlegroups throughout Europe
The fact that they felt sufficiently alarmed by Russian actions (and their history with them being less than stellar!) to do this just highlights both how much Putin overreached and NATO opinion of Russian strengths and weaknesses
Essentially Russia cannot do anything about this, and hasn't been able to do for a while, but by invading Ukraine they have told everyone that they don't care if they can't actually do stuff, they are willing to do it anyway