As real epxperienced user you can tell us how it need work.
I see system is working like this, after you select and activate app aircraft start follow route to iaf, no app still in progress. After passing iaf then fpl started follow app list, now you see only some kind of direct to iaf arrow inside fpl. If you initiate app all other fpl waypoints are ommited and fpl set route dct to iaf, this is now working system and from your video is clear that. How it then need work irl?
In simply way in this functional system you don’t need activate app till not reach iaf, aircraft will follow actual fpl, only after that iaf or leave sim initiate app automatically after reach iaf. Simply with my command Activate approach means approach start so to iaf direct start for first, then follow app list. I see this system as ok.
eeeehm forgot to say, this has nothing to do with gns addon probably, it’s sim system.