1) If I recall correctly it was not Google Photos app that was bugging you but when you came to attachments from an app it only went to Samsung gallery's so you could not attach a google cloud photos this way?
I understand this is because you have not granted Google Photos access to photo picker, just go to google photos, tap your icon, select photo settings, select apps and devices, select google photos access, select photo picker, select allow.
This should resolve your annoyance and you wont have to share now
I believe Photo Picker is the default api used by apps to attach photos
Whats not been implemented by Samsung yet but 4 other OEM's have (Xiaomi, Oppo, OnePlus, or Realme) is displaying Google Cloud Photos in the Samsung Gallery app
2) There are options and default settings you can change so the photo settings that are more suitable for moving objects, even for candid shots. But I agree the old sports mode was much easier.
3) Really colour Icons that has only been on an Iphone < 1 year and this is a deal breaker