Doesn’t bother me if they recline - on an Airbus the seat base pivots so you get more knee room.

Related things that do annoy me - people dropping the seat back with a lot of force (why not recline gently so the person behind can adjust their stuff?), and people kicking the back of my seat.

A 12 hour flight is often going to involve a change in timezone, so I usually get some sleep, and for that I want my seat reclined … plus keeping in one position for that amount of time is uncomfortable for my joints and backside.