Hi,
WordPress version 5.5 supports to sort, drag & drop meta boxes in the Block Editor. You can use this custom CSS code to remove buttons (up and down).
.handle-order-higher, .handle-order-lower {
display: none;
}
Apply the admin CSS code with this plugin https://wordpress.org/plugins/admin-css-mu/.
I'm going to create a feature request to support a setting of the meta box to remove sort buttons. Thank you.