Cheting

I do not know about Shadow Pokemon from trainers but the ones in the Rift Dens can definitely be shiny.

https://drive.google.com/drive/folders/1Ll-Z57X6pSVSHpPzqGcDwZ0mv8OjUzkd Terajuma Dragonite mail "quest".

"Q" and "W" are mapped to these functions since Version 13.(qwert keyboard)

Yes, most likely a bug. You are not the first to report that on the forum and the Google Doc about bugs.

Someone in the forum suggested going to Rhodea's apartment in order to fix the broken cycle. It worked in my case, so give it a shot?

Route 9 right hand side on the beach.

You can exit the place via the Rift entrance behind Angie and even return to Floria Island via the Yacht...

When you obtain HM Fly and return to Sheridan Village that ability of hers will be unlocked.

No, you can access the cave as soon as you reach Sashila for the first time. You just need to talk to the NPC who gives you permission to enter on the right hand side of the village. Go to the top and surf in order to reach him.

It sadly does not work.

Parasect are wandering around Darchlight Woods during daytime. They respawn after you leave and re-enter the area.

I could think of three things: Are you winning the battle after taking the required damage, is your Yamask a galarian one and are we having a misunderstanding because the link says for you to be in the Wispy RUINS and not Wispy Path?

https://www.rebornevo.com/forums/topic/56021-aeviumgalar-regional-form-evolutions/?tab=comments#comment-936940

The advanced Pokedex agrees. Magnet is listed there as Hold Item.

Moon Stone is not listed as Hold Item in the Advanced Pokedex, so sadly no.