I started with TR this year. Spent some time looking at related plans and different plans, reading and listening about training planning, and can searching the workout library. Between what i see in plans and searching, I have a handful of workout families like Pettit, Galena, etc., that are my go-to fillers or extra work workouts based on workouts I see in those plans. At least a couple of families per zone (endurance, SS, VO2) and duration, which are my main variables. I usually sort by TSS to narrow down to a specific section of results.
It takes some effort to get there, but I have a better appreciation of how a plan is built for the effort.