So I thought about bumping this up because I have just learned that it appears to be possible to book multi-city rewards, even though the option to do this has been gone for ages. Both the AF and KL mobile apps let you select multi-city as an option, and then turn on the switch to pay with miles. The multi-city approach seems to also make a difference on the pricing, so it isn't just two one-ways cobbled together.

Here is an example. YYZ-CDG-AMS on 21 Jan, with AMS-IAH on 30 JAN. If I try to do this as a multi-city booking, the total miles required come out to 120k plus EUR 598 in taxes+fees:




But if I try this as two one ways, the first flight drops down to 50k but the return segment remains the same. The total comes down to 100k points plus EUR 528 in taxes+fees:




The difference in miles and cash cost makes it pretty clear that multi-city ticketing is indeed possible with FB redemptions. But why the changes in pricing? Returns always price out the same as two one-ways, so why is this behaving differently? I know that the example I gave here is one where booking two one-ways is better value, but a user on reddit swears that they found a routing where multi-city was cheaper than two one-ways.