I have i7 8700k and RTX 3090. I can get 165 FPS (my monitors native refresh) while sailing and away from land but once I get into my main fortress I get around 80-90 FPS. 1440p.

I also lose major frames the longer I play the game and travel to multiple areas. One really long play session saw me start to average 60 FPS with dips into the 40.