look at : https://github.com/mayTermux/myTermux/blob/main/.termux/termux.properties#L22
the default shortcut for change session are CTRL + n.
but, you change it to CTRL + u. don't you know that shortcut for nano paste function?
even though it's posible to rebinding nano shortcut from .nanorc file.
just leave that as default, why doing a useless thing by change that shortcut?