How to Shiny Hunt in Dynamax Adventures :
1. Enter the Adventure and proceed through the raids.
2. Catch all the Pokemon (or at least the ones you would like to shiny check).
3. Check the screen where you select the mon you would like to keep with you. This is where you can see if a mon is shiny or not. If the mon has a shiny that's similarly coloured you can go into the summary screen to look for the shiny symbol.
4a. If the legendary is not shiny, choose a different pokemon and exit, then do another attempt.
4b. If the legendary is not shiny and you used any balls that you don't want to lose (apriballs, beast/dream/sport/safari balls), close your game and to do another attempt.
NOTES:
- If you soft reset with method 4b too many times, you will be asked to pay a fee to enter the den again. Not sure on what number triggers this penalty, whether it's permanent etc. The penalty is to pay Dynite ore to enter.
- Once you choose a mon to keep, the game saves.
- Also, the RNG roll for shinies, is per person. So if one person gets a shiny, it doesn't mean everyone gets that shiny. Both for the legendaries, and the normal mons within the adventure dens.
- You can also use this method to reroll for IVs. Just check the summary screen at the end of the raid and use an online IV calculator to approximate IVs. Make sure you don't select the legendary as the game saves after you select a mon.