Hi there. i just bought a garmin forerunner 265. i do pretty much all my winter riding indoors using my kickr. i run my trainerroad workouts through zwift. what id like to know is, is there anything i need to know about connections between garmin, zwift, TR and my trainer? do i need to start an activity on my watch or not? i dont want the watch to interfere with the trainer. ive connected my bike computer mid workout in the past during a recovery valley in a vo2 workout. big mistake. it took over the trainer and i have to do 4-500w just to keep the pedals turning destroying my recovery and ruining my workout. i dont want to make the same mistake with this watch. i rode today and did nothing with the watch. zwift connects to my chest strap hrm. my zwift, TR and garmin accounts are all connected. thank you for any insight
Your watch doesn’t need to know you have a trainer or use trainerroad/zwift.
The only thing you will probably want to do is make sure that your watch is now your primary training device so that you don’t have to sync a garmin device, like your bike computer, to get it to update the training metrics if you care about them. Your watch since it is sync’d to your phone presumably should handle this automatically.
Yeah. I don’t use my Garmin Edge or watch for trainer workouts. I just do the workout in TR (or Zwift, or whatever) and have that sync with Garmin Connect. Riding the bike outdoors, I’ll start and record the activity on my Edge or my watch, but not both. That then syncs with TR. On caveat. I’ll sometimes use my watch for HR, so set it to broadcast HR and have that paired just for HR with my Edge outdoors, or the TR or Zwift app indoors.
TrainerRoad and Zwift should be able to push to Garmin. The only metric that gets messed up is body battery if you don’t record an activity, either take the watch off while you ride or pair the watch to just the power broadcast from your trainer and not the trainer ftms controls (acronym might be wrong)
I’m just curious, what’s your goal with the watch here? I’m not sure I see the benefit of using a watch in this scenario.
Let me know if I’m missing something. 
no specific goal. i just want to make sure it doesnt interfere with my training connections. if theres some additional data i can get from the watch then great
i rode today and did nothing with the watch. zwift connects to my chest strap hrm. my zwift, TR and garmin accounts are all connected.
You answered your own question. Most of the time I don’t even bother wearing my 265 indoors. Continue to do nothing and you’ll be fine. The Zwift/TR workout will be pushed to Garmin Connect and that’s that. If you already have a HR strap then there’s literally no additional value the watch can provide in this scenario.
I agree with @idclark13 
I don’t think there’s much to gain by wearing another device, and there’s potentially some to lose in dealing with the signal interference/connection issues you’ll likely have when trying to throw another sensor in the mix. 
Don’t connect your watch to your trainer, pretty much at all or ever if you’re using TR to run/control your workouts. Basically remove the connection so your watch doesn’t know your trainer is there. That’s the solution.
IF you have a power meter on your bike (e.g. Quarq, Assiomas) then what you can do is connect the watch directly to the PM, while you run TR connected to your trainer, and then dual-record the session. You can then overlay them in a tool Like DCRainmaker Analyzer to see if your bike PM and Trainer are reading the same.
Odd one out here, but I dual record. While TR will push workouts to Garmin Connect (and Zwift) some of the challenges/badges in Garmin Connect will not be earned for workouts that aren’t recorded in the Garmin ecosystem. GC and TR do play well together for most of the analytics (Stress, Workout recovery, etc) but if you want all the GC stuff then you need to record it with a Garmin device or inside the GC App. 99% of the time the Garmin device just sits there and collects the info. The other 1% is when the Garmin loses signal with the trainer and it will “take control” which as you found out can interrupt the TR workout. It’s only occurred when using TR through Zwift for me. If I’m using the TR App I haven’t had an issue with the Garmin device taking control. I only connect for as a power/speed sensors and not trainer control. Hope this helps.