Hi There,
Why ANY can't be used? Do you get an error when using ANY?
Just set the Primary Uplink for WAN1, disable load balancing and you have the entire network using WAN1. No need for Flow Preferences to be set.
If you really want to keep WAN2 and use the flow preferences you would replace the destination of 0.0.0.0/1 with ANY just like on the screenshot.

MX Load Balancing and Flow Preferences
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