NetworkManager supports a `slaves-order` option in NetworkManager.conf to control the order of activation of ports at boot.

slaves-order
This key specifies in which order slave connections are auto-activated on boot or when the master activates them. Allowed values are name (order connection by interface name, the default), or index (order slaves by their kernel index).

This property was introduced only to allow keeping the old behavior in RHEL7, while the default order was changed from `ifindex` to `name` in RHEL8. The usefulness of this option is questionable, as `name` together with predictable interface names should give a predictable order. When not using predictable interface names, the name is unpredictable but so is the ifindex. And in any case, interfaces can appear at any time and so the concept of "order" is not very useful.