I agree that the whole identity verification stuff is confusing in element. I think it would be less so if they just generate and present the backup security key at account creation, telling users to use this when they want to login on a different device and drop the whole ad-hoc 'scan a qr code' process.

Having said that, is the UI/UX apart from the above really terrible? When using as a simple messenger app, the experience for me is almost the same as WhatsApp (which almost completely replaced sms at least in the Netherlands). The biggest issue I have is that when you open the emoji selection screen when typing a message, you have to close this and reopen the keyboard to continue typing, which is a bit silly, but not a deal breaker.