I had a very bad experience with my BT headphones so far:
JBL Inspire 500 -> Bad in any way and doesn't work wit fenix (dropouts)
Vivianco Outdoor -> basically not bad but doesn't work with fenix (dropouts)
Samsung Galaxy Buds -> Best headphones of all time but sadly also dropouts with fenix
Now I bought JBL Reflect Mini 2 and they work absolutely flawless with the fenix, no dropouts at all and for a price of about 70€ very solid headphones with good sound and absolutely stable in the ear during workouts. If you don't mind the cable and don't want to spend too much I can totally recommend these. The previous model is also on the (very short) list of Garmin recommended headphones.
it's a small sample size, but I ran for the first time with my AirPod (only wear 1 bud and in the right ear) and my 5X Plus today (worn on my right wrist). I had 0 issues (connected quickly, no drop outs, etc.) for over an hour.
Just got Powerbeats Pro. Work very well no dropouts. Just watch for wind noise.
Jabra elite is enough nice but bit pricy. That's the cause I am using Xiamoi airdot pro and next month I will take Skullcandy indy.
I user Jabra Elite Active 65t but they have also problems with stable connection. Music is often not in sync and music jump in a song. Sometimes it works for 10 minuten.
Check it, these are the best alternative of airpods. protechbound.com/.../