How often do you need to lubricate alloy seat posts
No they won't. It is often enough to lubricate once when the bike was built unless it is used/kept for a very long time. Especially if the bike is kept in a dry place. It is not necessary to lube it once a year. The lube stays there and protects the interface for a long time. If you pull a bike that hasn't been used for ten years from a shed, many things could be seized but even then seizing of the seat tube is far from guaranteed. It is even unlikely if it was well conserved before the storage.

Interface of two different metals could change it due to electrochemical potentials and rusting. I assumed aluminium alloy on both sides or steel on both sides.

Just do it the next year or when you get to your bike.