You’ll probably get better advice over here : The Short Course Triathlon Thread
But personally (as a beginner/3rd year triathlete) I’ve already started my off season! My general plan is to spend a few weeks doing whatever I feel like; gravel riding, MTB, trail running, then have some time establishing good habits doing the things I’ve been meaning to add in - more yoga, strength and flexibility stuff.
As well as the background conditioning work I’ll probably do one or two short blocks working on some of my weaknesses - swimming technique or shorter faster runs.
For me off-season is about having a break, then having time to work on weaknesses AND start building foundations for the next season. Doing just a bike plan and adding occasional swim/run sessions might not be the best use of the time if you’re already a strong rider (obviously ignore this if you’re an ex high level runner/swimmer!)