Just to add a couple of ideas, although I haven't used a GoPro on my touring bike.
Consider a smaller handlebar bag that offers you some adjustment re how high you mount it. My favorite handlebar bag of all time is the small Topeak Compact Handlebar bag. Converts to waist pack if you want to off the bike. Great mounting kit that also comes w/ a round plastic insert for mounting your GPS, bell, etc. Holds the important stuff that you should take w/ you when you leave the bike. Given it's size, can be mounted "pushed down" if necessary and doesn't interfere w/ cables. In higher position, you can easily also run bikepacking style frontloader bag for tent, etc. underneath the handlebar bag. Drawbacks for some...it's not waterproof like an ortlieb (comes w/ rain cover) and doesn't have clear map holder. I don't care about the lack of either feature (YMMV). Decent chance a stem cap mounted GoPro would clear...but you might have to change the stock mount that's on your Trek. No guarantees
[By the way, my underlying bias is that I do not care for overly large handlebar bags for numerous reasons that are beyond the scope of this thread!]
If you are rocking a newer touring bike, you might be lucky to have many cage/accessory mount bolts up front on your fork, etc. Hopefully some are unused, in which case put on a Paul Gino mount (pricey) or Origin 8 Eyelet Stub (what I have) to give you more and often better mounting options. So I run "anything" style cages on my fork nowadays instead of my former lowrider front pannier rack, so I have free rack mount holes near front axle. I installed an Origin 8 mount on outside of left fork leg, near hub and have my headlight there. Simply fantastic field of light, and does not blind oncoming motorists, cyclists or pedestrians (as handlebar mounted lights often do...especially if they are designed for offroad riding).