Hi
@Reens80 and welcome to the forums.
Firstly, congratulations on your pregnancy.
I've experienced pregnancy as a T1 diabetic (so insulin all the way), albeit in the years before continuous glucose monitors were available, so I can say from personal experience that though it's best to keep blood sugars as normal as possible the odd spike certainly didn't harm my babies.
I use a dexcom G7 , wich I believe is very similar to the ONE but has a few more features (it links to my insulin pump). So, assuming that the add note feature is the same
1) I log exercise as however many minutes I do, with the start time when I start the exercise. (The G7 lets me edit the time when I add a note). But honestly, I suspect it doesn't matter what you do as long as you tell your DN and do it consistently.
2) I log my meals when I start them, but this is something you should probably check with your DN.
3) I personally don't know about other apps but hopefully some other people will post soon and advise.
Please try not to stress too much about the GD, I appreciate it's scary, particularly when you are new to diabetes. People have been having successful pregnancies with GD for decades and decades, and though the new tech allows for better monitoring and hopefully better results, sometimes I wonder if the additional stress caused by the overload of information is counter productive. (When I was delivering my first child, I shared a ward with a woman who was having her third child with GD, and she and the baby were both fine.)
Once more, congratulations on the pregnancy, and welcome.