The Dynamic Naming dialog can say:

"Naming has to be formed using dynamic items (such as [title] or
[track]) otherwise every track will have the same filename."


even when there is only one track. This needlessly prevents the user specifying a valid name consisting of e.g. [encoder].

Workaround: enter the name pattern instead in Output Location, Dynamic since (inconsistently) this is now checked as above) e.g.