Well, it is not like you have to start at square one, but you definitely do not pick up where you left off.

Unless you have the type of brain that analyzes the entire position every time, then you build up a game in your mind, and the part that is rusty is the piece that recognizes all the dangers.

The game of chess today is not the same as it was 25 years ago.

Bobby Fischer was brilliant, way ahead of the people in the same era. But i doubt he could work well against StockFish if he were alive still.

Magnus Carlson had a tough time early on against the computers of today, but he learned a lot of techniques from it. Like denial of pieces because of blocking off their usefulness. It is like taking a piece from the board without taking it.

The meta-game has seriously shifted in the past 25 years.