Locking down a website to only be available to users on Apple and Windows doesn't make it safer. It just reduces the cost of building it because you don't have to bother testing it on any other platforms. Rather than tell users "Danger, we haven't tested your choice of OS" companies prefer to lock it down.
Users on Apple and Windows are not safer because a bank has chosen to block Linux.
Until they decide to force you to use the mobile app as a 2FA for the website. My bank did that, I literally had to buy a new phone because the old one couldn't update their stupid app. It locks you in to the latest N versions of Android/iOS.
Before you ask, no, other banks aren't any better where I live. They all stopped using physical 2FA keys years ago. And no, they won't let you come in physically for things that can be done online.
Users on Apple and Windows are not safer because a bank has chosen to block Linux.