About a week ago I opened Hearthstone on my iPhone 14. I only play on this phone. The normal screen popped up except instead of the mode screen it prompted me to switch accounts. Figuring it was just a bug I shut it down and reopened it only to have the same screen displayed. I deleted the app and redownloaded it as I have dozens of times over the years only to have it open as a new account. I clicked the tab to sign in and it prompted me to sign in through Battlenet which I tried to. I was able to sign it and it says it recognizes my account but says I must switch accounts to play. It’s an endless loop that won’t let me access the game. I opened a ticket with Blizzard and the advice I got was to log out of Battlenet and then reset my password. I’ve done that multiple times and no luck. They then suggested that if that doesn’t work to post here in hopes someone could help. I have been a nearly daily player for seven years and have a complete standard collection minus a couple meaningless legendaries. I get legend most months. I have many complete golden decks. I always buy the mega bundles, rewards tracks and mini sets. This is my #1 hobby so I’m not shy about spending money on it and love the game (most of the time). The thought of having to start over with a new account bums me out because of the money and mainly time I’ve put into the game. I’m fairly active in the social media community and have friends who do Hearthstone podcasts so I have other people I can contact but thought this might be the best place to start since submitting a ticket didn’t solve this. I don’t know if my account got hacked or this is just some kind of weird bug but I really appreciate any help you guys could provide. Thank you.
I was having this exact issue myself and I found a solution that worked for me; wanted to share to hopefully help you or anybody else dealing with this.
Instead of trying to sign in, sign up for a new account with either a throwaway email or something like that and then switch to your actual one. The idea is that if someone has offline unsaved progress and logs into an account, it doesn’t know which account’s progress to prioritize, so it won’t let you overwrite it. The problem is it considers skipping the tutorial to be progress worth keeping, so you have to make an account and then switch from it to your normal one.
Hope this helps, I stayed up pretty late trying to figure this out because of how abhorrent blizzard designed this system.
Sign in to battle.net.
Go to connections and add either google or apple account.
Open the hearthstone app.
Press sign up instead of sign in.
Sign up with your added google or apple account.
Worked for me, don’t know why.
Feels weird this problem still persists…
I had the same problem and i found a way that helped me.
First i skiped the tutorial. Then i went to options ingame and press change Accounts.
I could not change for a europ account so first i changed to an america account.
Then i tried again and i could choose europ and log in with my account.
I hope it helps and sry for my english 
Thanks, this approach helped me ^^