Looking at the
document you linked in the USA/Canada Delivery Thread the submission to the NHTSA is related to the V6 rather than the I4, it does not guarantee that US I4s will have the M designation, they could add alternative letters down the line when submitting the paperwork for the I4 variant.
M for 298kW is supported by the interior image posted by
@lynchy73 above as the VIN is visible on the door pillar sticker. This does contain M in the engine position for a 400hp Chinese market car. What it could be is that the M is included in the decoder because that variant is currently the only other variant in production currently.
Conversely there is a VIN against my UK spec I4 order on My Lotus and this has a K in the engine position which does suggest a different variant. However, it does also have a P in the MY position (MY24 is R) so I expect with the delays to production the VIN probably isn't final until the car eventually does hit production.
It's just an artefact of converting kW to hp and not rounding to the nearest integer (which would be 400).