After struggling to get this to work all day I can finally validate a work around to anyone experiencing game share problems!
Requirements: 2 controllers
Make sure both the account that purchased the game, and the account you’re trying to share with are on the same console
Start diablo 4 on account that purchased the pre order
If a character has already been made, must create a new character on account that has purchased the game, at this point before starting turn on second controller and sign into account you want to GameShare with (should get a message stating player 2 can join once player one starts the game)
Once new game has started on account that purchased the game, join in as player 2 on the 2nd controller
Leave game on controller player one was signed into, and bam! It lets you stay!
Link to my twitch if you need proof or live help!
Also shoutout to perendia for discovering if you don’t have a second controller you can use your phone with the ps remote app!