Do range hood inserts with rear exhaust exist?
I have an older Bosch unit that was sold with both inserts, however:

Standard fans usually have pretty weenie capacities and putting a 90 degree bend will seriously affect their flow. This is why cheaper, low capacity hoods only come with straight inserts. Ironically, many expensive, snazzy looking, hoods have miserable performance.

High capacity hoods with beefy fans tend to be a lot more money, but will have the overhead (ha ha!) to accomodate bends and longer duct runs.