Disable automatic rearrange ios
This is not possible on an un-jailbroken iOS device.

The apps in the app-switcher are sorted by how recently they were last open (most recent on the left). You can not modify this behaviour.

The app-switcher is designed to let the user open apps that they used recently. It isn't designed to open a user's favourite apps - that's the home screen's job.

Try to organise your most-used/favourite apps together on one page on the home screen for quick access.