On a Mac you can delete ~/Library/Cookies/HSTS.plist file and restart Safari to fix this, not sure how to do that on mobile, you could use Firefox or Brave.
The app has been updated in the apple store with an update note that says he added an app id to fix Lemmy.ml issues but it does not seem to work. I’m guessing that there is something Lemmy.ml has do whitelist now.
On a Mac you can delete ~/Library/Cookies/HSTS.plist file and restart Safari to fix this, not sure how to do that on mobile, you could use Firefox or Brave.