However, are you talking about some specific SMF exporter? I haven't seen any on the SMF side!
They're probably talking about nodebb-plugin-import which works alongside an exporter plugin like nodebb-plugin-import-smf by providing a common API for the exporters to use (and yeah, exporter plugins have import in the name... Makes a bit of sense since nodebb-plugin-export-smf would suggest it's exporting to SMF, but it's still a bit weird)
I'm not sure how well maintained that is honestly, but NodeBB database schema hasn't seen any major changes in the last few years - still, the best idea might be to follow what the readme offers, install NodeBB 1.12.1, import data from SMF and then upgrade NodeBB to 3.x. Though note that you'll probably want to switch to Harmony theme after upgrading, since you'll be defaulted to the old Persona theme 🙂
The bigger question is whether the SMF plugin will work with 2.1.4, since it was tested on 2.0.3 and hasn't been updated in the last few years