Thanks Everyone it worked perfectly. The SD card was formatted in exfat. I didn't try to format the 64GB in FAT but formatting another one 32GB in FAT did the job.
And thanks Scott for birdseye I can now have birdseye imagery on the SD topo 24K North East and I will upload birdseye imagery on another SD card for topo Canada.
I used the Oregon 750t in the Adirondacks. But I was not really used to it. Besides I uploaded the full track of Big Slide mountain I found in Adventures and a lot of geocaches. Unfortunately we had to pick another mountain (Giant) because the parking was full.
Even if it's easy to work with at one point we were walking and talking my little daughter and me so I didn't look around. All of a sudden we were no longer on the trail, the clouds were rolling out of nowhere, it was dark. I think I understand how people can get lost even when they're hiking on trails.
Unfortunately the friend we were hking with and his kids was so anxious to get the summit fast (hiking is racing for some people but my little one likes to take her time, observing the nature around, geocaching when we can) I didn't enter a waypoint at the beginning of the trail.
Nothing to panic about at this point because I could have found my way back I think. I took a moment to show her how to use backtrack. But it was a little confusing because I had 2 tracks for a reason or another. Of course I used the latest one. The map was now showing up, I didn't know why. I figured something out.
However, I'd like to find a better user manual than the one Garmin made, explaining only the basic. I've been trying to find better documentation or videos for the 700 series and even for the 650. So far I'm out of luck. If you know where I could get good documentation or video on the Oregon please let me know
And thanks again