My 2-cents, and the protocol I will be using this year is weight training 2x per week on riding/training days.
If my calendar calls for a high intensity workout, I will do the lifting after the trainer. If the plan calls for an endurance ride, I will do the lifting before the workout – so rest days are true rest days.
Last year I lifted 2x a week on days I didn’t ride. The combination of not being able to ride on lifting days, and then not being able to handle on-bike workouts with any intensity the day after lifting caused me to be in a year long FTP plateau. On the plus side – I feel great and looked better than I had in years.
I lift for whole body health, the mirror/vanity, concerns about bone density (I’m 44) and injury prevention. I’m not necessarily looking for it to make me faster on the bike, I’m just trying to make sure it doesn’t limit the quality of my on-bike time. Maybe that’s a quixotic pursuit . . . we’ll see.
One other non-scientific tip: pick only one or MAYBE two lower body workouts that tax glutes/hamstrings as much as possible. Walking power lunges and deadlifts are my go-to moves. Don’t do 4-5 different lower body workouts as you would if your were truly “lifting”.
I used to only play sports where weight training was necessary and helped you…football/basketball. I struggle with the idea that strength training is a detriment in this sport. At the end of the day, I would sacrifice ~10 watts of FTP to look good/feel good if necessary . . . but I keep trying to convince myself that I can find the balance and don’t need to sacrifice.
Last thing of note, my “lifting” routine is only 45 minutes in length, and includes a bunch of push-up variations, bar dips, pull-ups with multiple grips, core work and then then the aforementioned 1-2 leg lifts. I have bad endurance genetics (sigh), but I have really good strength genetics and this is enough for me to add the upper-body strength/definition I want. I don’t need to get under a bar to achieve that. I recognize that others might be different.
Good luck everyone.