I don't really get what you mean by keyboard can be compromised by account synchronization. Also, I don't think there's any such thing as offline keyboard. To avoid losing your funds to scammers, do not install fancy or third party keyboard, only use the factory installed stock keyboard.
Some third-party keyboards come with account synchronization and sometimes such keyboards can also have keyloggers attached to them which means that anything you type using the keyboard, is sent directly to the hackers that have injected the keylogger into that keyboard and you wouldn't even know about it. Before you come to know, they will have your accounts emptied and you will have nothing else to do than to regret.
Mobile applications are getting compromised a lot these days, so users need to be cautious when installing applications both from app stores and from third-party websites because they can contain malware and other material that can compromise their device and financial apps.