You do realize Russia launched this invasion into Ukraine partly from Belarus
Why your call Putin would invade it?
He’s already there whenever he likes
The actual surprise in this why he doesn’t take the peach Odessa yet
It’s his if he wants it
The populace is split around one third Russian and the rest uke and Romanian and Bulgarian
Many think the Russians are coming for it any second
Putin wants to revoke the Belavezha Accords and reconstitute the USSR. Belarus was part of the USSR so it simply follows that at some point Putin will act to annex Belarus.
I would hope that this happens peacefully but from where I sit it looks to me like Lukashenko wants his forces to be able to fight the Russians if they need to. Otherwise Lukashenko would be sending his troops into Ukraine.